Why is my heating not working?

[mkn777er]

I wonder if anybody can help me with this? After about a year of ownership of my boat I am confident that I can get the Bubble stove 'burning and turning'. It works well, nice blue flame etc. what I cannot do, is get it to warm the water and subsequently the radiators!

 

This is what happens. It is fitted with a back boiler driving 3 radiators and a bathroom towel rail - fairly standard I believe. It has a 12v circulation pump which is either on or off via its own switch. I was told to never have the fire running without the pump on because that would quickly lead to the boiler boiling over! But here's the thing. I get the stove going, switch on the pump (I can hear it running) and everything stays cold, including the back boiler - I can very comfortably grab hold of the inlet and outlet pipes to the boiler and they are cold. If I then turn off the pump, the boiler quite quickly warms up and after say 10 - 15 mins switch the pump back on and warm water then surges through the system, for about 5 mins before it goes cold again!

 

I have also discovered that if I use the immersion heater from the shore-line it will also warm the radiators because presumably the central heating system coils through the calorifier - same result with the engine running.

 

So in summary (at last!). Is this system set up correctly? Should the pump run continuously or cycle, because it seems to me that its pumping the water around the system before the boiler has chance to heat the water.

 

Thanks in anticipation!

[WotEver]

It sounds to me like a problem with the Bubble insofar as it doesn't appear to be appreciably heating the water in the back boiler. I know nothing about them so shall await someone with experience of Bubbles to offer a suggestion.

 

Tony

[Ex- Member]

Your 12v pump is running too fast, water is going through so quick it's constantly cooling the boiler. There should be an adjustment on the 12v pump to slow the flow. We have a 240v pump and that not only has to be on the lowest speed setting but the valves also have to be partially closed too.

 

Is the system up to pressure also around 1 bar, there should be a gauge under the accumulator tank.

[Tony Brooks]

.

 

Is the system up to pressure also around 1 bar, there should be a gauge under the accumulator tank.

 

I very much hope not - unless the Bubble is thermostatically controlled. Sealed, pressurised systems with stoves are a recipe for an explosion. I would expect the system to have an open header tank. I defer to anything MTBM says but I do not think the pressure in a sealed system has anything to do with circulation as long as there is sufficient water in the system. It is there to top up any minor weeps and to allow for the expansion of the water.

 

I suspect a pipe-stat (heat to make) on the upper boiler pipe controlling the pump with a switch in parallel for use in case of state failure would also help by not circulation cold water through the boiler.

[Ex- Member]

 

I very much hope not - unless the Bubble is thermostatically controlled. Sealed, pressurised systems with stoves are a recipe for an explosion. I would expect the system to have an open header tank. I defer to anything MTBM says but I do not think the pressure in a sealed system has anything to do with circulation as long as there is sufficient water in the system. It is there to top up any minor weeps and to allow for the expansion of the water.

 

I suspect a pipe-stat (heat to make) on the upper boiler pipe controlling the pump with a switch in parallel for use in case of state failure would also help by not circulation cold water through the boiler.

 

Been through all this before. this type system is installed in millions of homes, none have Exploded to my knowledge Ours has been running 7 years without issue. Technology moves on you know

 

The system fully complies with any BSS requirements as well.

Edited October 29, 2013 by Julynian

[Tony Brooks]

And ALL of those in homes use thermostatically controlled boilers most of which, if not all, have an additional overheat shutdown. If the Bubble is thermostatically controlled then fair enough, if not then it is potentially unsafe.

 

The BSS is no guide to safety within the boat, it is mainly interested in protecting the environment and third parties.

 

Pleas do not add suggestions unless you can be sure you are not confusing people. The accumulator tank you refer to is, I assume, the one specifically used to provide expansion space and a reserve of water for the central heating system NOT the tank most boaters would associate with being an accumulator. The "normal" accumulator should have no effect on the heating system.

 

Whatever you may choose to think it remains a fact that unless a boiler of any sort is thermostatically controlled with some overheat back up it is potentially dangerous to use a sealed, pressurised system. You can not extrapolate from domestic practise to that applied to boats.

[Ex- Member]

And ALL of those in homes use thermostatically controlled boilers most of which, if not all, have an additional overheat shutdown. If the Bubble is thermostatically controlled then fair enough, if not then it is potentially unsafe.

 

The BSS is no guide to safety within the boat, it is mainly interested in protecting the environment and third parties.

 

Pleas do not add suggestions unless you can be sure you are not confusing people. The accumulator tank you refer to is, I assume, the one specifically used to provide expansion space and a reserve of water for the central heating system NOT the tank most boaters would associate with being an accumulator. The "normal" accumulator should have no effect on the heating system.

 

Whatever you may choose to think it remains a fact that unless a boiler of any sort is thermostatically controlled with some overheat back up it is potentially dangerous to use a sealed, pressurised system. You can not extrapolate from domestic practise to that applied to boats.

 

Well obviously bubble stoves are thermostatically controlled, there are also other safety measures like pressure relief valve. The lack of pressure might not affect flow but can affect how rapidly water heats up, so clearly a point worth making and relevant to the op's question.

 

I think making rash statements like "recipe for explosion" following a caveat such unless is thermostatically controlled is rather like having more interest in scare mongering rather than actually assisting the op in their initial question.

 

You did the same a couple of years ago I recall, old habits die hard it seems

[nicknorman]

If the bubble has thermostatic regulation of the water jacket temperature, plus an additional overtemp sensor, (as domestic boilers do) then I agree with Julynian, otherwise I agree with Tony!

 

Anyway, back to the OP, how long have you left this running? If the water is circulating through some rads and a cold calorifier, it will probably take an hour or so for the rads to get hot because a lot of the heat will be going to the water in the calorifier. If I start our Mikuni (4.5 kw) it takes quite a few minutes for the water exiting the boiler to feel even vaguely warm, and longer if the circuit to the calorifier is open. However, after maybe an hour, the rads get very hot and after maybe 2 hrs the Mikuni shuts down to 1/2 power because the calorifier is no longer taking any heat and the rads can't dissipate all 4.5kw at 80deg C.

 

I refute that the water can be flowing too fast to transfer the heat. Physics doesn't support such an idea. If the water is flowing fast then INITIALLY the outlet water will be cooler because the heat is being more rapidly distributed through the system, but after say 30 mins the system temperature will be the same as it would have been with a slower flow.

 

Another question, how old is the back boiler? If its old, perhaps there is lime scale inside which is significantly reducing heat transfer from flame to water.

Edited October 29, 2013 by nicknorman

[Tony Brooks]

So you did not read my first 11 words, are you being deliberately argumentative? My caveat was there in my first answerer - where is yours?

 

Please now explain the physics behind your assertion that the pressure in the system can affect how rapidly the water warms up. I do not believe that you can because the rate of warm up is dependant upon the volume of water and the amount of heat being being supplied. Nothing to do with the pressure PROVIDING the system is full of water but even if it were not as long s the pump could circulate the water through the boiler the pressure will still not have an effect. The only thing the pressure will affect is the boiling point.

 

Now, as far as assisting the OP. Where did he tell you that he had a sealed heating system with a pressure vessel? Sending him looking for an "accumulator" that may well not be there is not so much help either.

 

Yes, if anyone suggest that it is safe for a stove that we have no knowledge off the full controls to run with a sealed system I will continue to warn of the danger. Especially when others suggest that it is safe and good practise.

 

Perhaps you can also explain how the pressure in a sealed system that is boiling will be contained.

 

I have not even mentioned the difficulty in refilling the sealed system with liquid containing anti-freeze unless you also buy a pump. That in itself would in my view suggest they are not best suited to boat use where DIY is far more common than at home.

[Ex- Member]

If the bubble has thermostatic regulation of the water jacket temperature, plus an additional overtemp sensor, (as domestic boilers do) then I agree with Julynian, otherwise I agree with Tony!

 

Anyway, back to the OP, how long have you left this running? If the water is circulating through some rads and a cold calorifier, it will probably take an hour or so for the rads to get hot because a lot of the heat will be going to the water in the calorifier. If I start our Mikuni (4.5 kw) it takes quite a few minutes for the water exiting the boiler to feel even vaguely warm, and longer if the circuit to the calorifier is open. However, after maybe an hour, the rads get very hot and after maybe 2 hrs the Mikuni shuts down to 1/2 power because the calorifier is no longer taking any heat and the rads can't dissipate all 4.5kw at 80deg C.

 

I refute that the water can be flowing too fast to transfer the heat. Physics doesn't support such an idea. If the water is flowing fast then INITIALLY the outlet water will be cooler because the heat is being more rapidly distributed through the system, but after say 30 mins the system temperature will be the same as it would have been with a slower flow.

 

Another question, how old is the back boiler? If its old, perhaps there is lime scale inside which is significantly reducing heat transfer from flame to water.

 

I refute that the water can be flowing too fast to transfer the heat. Physics doesn't support such an idea. If the water is flowing fast then INITIALLY the outlet water will be cooler because the heat is being more rapidly distributed through the system, but after say 30 mins the system temperature will be the same as it would have been with a slower flow.

 

 

 

It's not that it won't transfer heat, it's more the time it takes.

 

When initially setting up our system we had exactly the same problem. It would take hours even for the rads to get luke warm. The on site plumber told us to slow down the flow rate, in addition don't switch the water pump on until the stove fully heats. We did as he suggested and the rads began warming much quicker. Another point to make is if your bubble heats the calorifier too, isolate it if you want to get heat in the boat quickly.

 

Since doing this our rads begin to warm in about 15 minutes then slowly rise in temperature over the next hour.

[nicknorman]

But you changed several things at once - keeping the pump off until the stove is hot, turning off the calorifier circuit, and reducing the flow rate. The first two will obviously increase the warm up speed from the time when the pump is switched on. The final one won't increase the overall heating rate of the system. What I suppose it may do is redistribute the heat in the system - making the 1st radiator in the circuit get warmer at the expense of cooler rads further back. If this is the aim, then fine. But heat transfer from the boiler is not going to be significantly improved by reducing flow rate.

[Ex- Member]

So you did not read my first 11 words, are you being deliberately argumentative? My caveat was there in my first answerer - where is yours?

 

Please now explain the physics behind your assertion that the pressure in the system can affect how rapidly the water warms up. I do not believe that you can because the rate of warm up is dependant upon the volume of water and the amount of heat being being supplied. Nothing to do with the pressure PROVIDING the system is full of water but even if it were not as long s the pump could circulate the water through the boiler the pressure will still not have an effect. The only thing the pressure will affect is the boiling point.

 

Now, as far as assisting the OP. Where did he tell you that he had a sealed heating system with a pressure vessel? Sending him looking for an "accumulator" that may well not be there is not so much help either.

 

Yes, if anyone suggest that it is safe for a stove that we have no knowledge off the full controls to run with a sealed system I will continue to warn of the danger. Especially when others suggest that it is safe and good practise.

 

Perhaps you can also explain how the pressure in a sealed system that is boiling will be contained.

 

I have not even mentioned the difficulty in refilling the sealed system with liquid containing anti-freeze unless you also buy a pump. That in itself would in my view suggest they are not best suited to boat use where DIY is far more common than at home.

 

As I said been through it all before, find the old thread, I really can't be arsed.

 

I will say though, why use a caveat like that on a stove that's been designed to be used in boats and has been for years, and I don't know of any diesel stove with a back boiler that wouldn't have safety cut off equipment. I would have thought someone of your knowledge would know this very well, but in order to scare monger and again show your disapproval of pressurised systems, you chose to use a caveat to try and make a point that has no validity

[ditchcrawler]

If the bubble has thermostatic regulation of the water jacket temperature, plus an additional overtemp sensor, (as domestic boilers do) then I agree with Julynian, otherwise I agree with Tony!

 

Anyway, back to the OP, how long have you left this running? If the water is circulating through some rads and a cold calorifier, it will probably take an hour or so for the rads to get hot because a lot of the heat will be going to the water in the calorifier. If I start our Mikuni (4.5 kw) it takes quite a few minutes for the water exiting the boiler to feel even vaguely warm, and longer if the circuit to the calorifier is open. However, after maybe an hour, the rads get very hot and after maybe 2 hrs the Mikuni shuts down to 1/2 power because the calorifier is no longer taking any heat and the rads can't dissipate all 4.5kw at 80deg C.

 

I refute that the water can be flowing too fast to transfer the heat. Physics doesn't support such an idea. If the water is flowing fast then INITIALLY the outlet water will be cooler because the heat is being more rapidly distributed through the system, but after say 30 mins the system temperature will be the same as it would have been with a slower flow.

 

Another question, how old is the back boiler? If its old, perhaps there is lime scale inside which is significantly reducing heat transfer from flame to water.

I knew I could rely on you Nick, saves me a lot of typing.

[Hawkmoth]

But you changed several things at once - keeping the pump off until the stove is hot, turning off the calorifier circuit, and reducing the flow rate. The first two will obviously increase the warm up speed from the time when the pump is switched on. The final one won't increase the overall heating rate of the system. What I suppose it may do is redistribute the heat in the system - making the 1st radiator in the circuit get warmer at the expense of cooler rads further back. If this is the aim, then fine. But heat transfer from the boiler is not going to be significantly improved by reducing flow rate.

Agreed!

[nicknorman]

I'm not sure the bickering is helping the OP!

 

FWIW having the pressure in the system at say 1 bar, vs say 1/2 bar makes zilch difference. Yes higher pressure does increase the boiling point and reduce propensity for cavitation in the pump but a normal system would not be approaching either of those limits.

 

Very low pressure is to be avoided because it means there is no reserve coolant in the accumulator and without a header tank, you are therefore close to letting air into the pipe work.

[Ex- Member]

But you changed several things at once - keeping the pump off until the stove is hot, turning off the calorifier circuit, and reducing the flow rate. The first two will obviously increase the warm up speed from the time when the pump is switched on. The final one won't increase the overall heating rate of the system. What I suppose it may do is redistribute the heat in the system - making the 1st radiator in the circuit get warmer at the expense of cooler rads further back. If this is the aim, then fine. But heat transfer from the boiler is not going to be significantly improved by reducing flow rate.

 

Not initially we didn't as the calorifier was fitted much later. If we open the calorifier it takes much longer for the boat to heat up for obvious reasons, so we only put the calorifier on when the heating is up to temp. This way you hardly notice any difference in all round temperature as the calorifier heats up.

 

Just reducing the flow rate though definitely heats the boat much quicker

[nicknorman]

Just reducing the flow rate though definitely heats the boat much quicker

 

Could you explain how this can be so?

[WotEver]

Please sir, can I answer?

 

It can't.

 

Tony

[Ex- Member]

Could you explain how this can be so?

 

No Haven't a clue. It does though simple as. My theory is that flowing fast the water gets very little heat at all so cools quicker as it returns to the pump even though it does quicker.

 

With a slower flow the water is initially much hotter and warms the rads & pipework quickly so maintaining heat in the infrastructure as more flows.

Edited October 29, 2013 by Julynian

[nicknorman]

Transfer of heat energy through a heat exchanger such as a back boiler, is proportional to the temperature difference between the hot side, and local coolant temperature , assuming other things such as surface area of the exchanger remains constant.

 

With fast flow, the inlet and outlet temperatures will be similar, with the temperature difference determining the heat transfer as previously mentioned.

With slow flow, the outlet area will be hotter (reducing heat transfer) whilst the inlet area will be cooler (increasing heat transfer). The increase and decrease balance out so that the overall heat transfer is the same as the fast flow case.

 

In fact there is a further factor - with slow flow, the flow may be laminar which results in poorer heat transfer, whilst at higher flow rates the flow will be turbulent - a chaotic mixing of the coolant within the boiler which aids heat transfer.

 

As an experiment, get your system up to temperature, then measure the temperature of the rads. Now double the flow rate and measure the temperatures again. You might find that the 1st radiator is now a little cooler, but the last radiator will be correspondingly hotter with the average remaining constant. The rate of heat transfer from the boiler will remain the same

 

The effect you perceive is probably because the first radiator gets hotter quicker and that is in the room you are occupying.

 

But any feeling that the overall heating up rate is improved would require new laws of thermodynamics and since the old ones have sufficed for quite a long time, I'm inclined to go along with them.

[smileypete]

Sounds like the OP is trying to run too many rads for the output capability and heat setting of the stove, maybe try just one to begin with? Though could also be worth checking the heated surface of the back boiler is free of soot deposits.

 

Agree with Tony Brooks BTW, only run pressurised if the mfr explicitly allows it and their instructions are followed to the letter. Even so still far better to use a header tank, as the *rse kicking consequences of getting things wrong are much less.

 

cheers, Pete.

~smpt~

Edited October 29, 2013 by smileypete

[Ex- Member]

Transfer of heat energy through a heat exchanger such as a back boiler, is proportional to the temperature difference between the hot side, and local coolant temperature , assuming other things such as surface area of the exchanger remains constant.

 

With fast flow, the inlet and outlet temperatures will be similar, with the temperature difference determining the heat transfer as previously mentioned.

With slow flow, the outlet area will be hotter (reducing heat transfer) whilst the inlet area will be cooler (increasing heat transfer). The increase and decrease balance out so that the overall heat transfer is the same as the fast flow case.

 

In fact there is a further factor - with slow flow, the flow may be laminar which results in poorer heat transfer, whilst at higher flow rates the flow will be turbulent - a chaotic mixing of the coolant within the boiler which aids heat transfer.

 

As an experiment, get your system up to temperature, then measure the temperature of the rads. Now double the flow rate and measure the temperatures again. You might find that the 1st radiator is now a little cooler, but the last radiator will be correspondingly hotter with the average remaining constant. The rate of heat transfer from the boiler will remain the same

 

The effect you perceive is probably because the first radiator gets hotter quicker and that is in the room you are occupying.

 

But any feeling that the overall heating up rate is improved would require new laws of thermodynamics and since the old ones have sufficed for quite a long time, I'm inclined to go along with them.

 

 

The effect you perceive is probably because the first radiator gets hotter quicker and that is in the room you are occupying.

 

 

 

Quite possibly, we are very open plan though and the heat up time difference between the fastest pump speed setting 3 and slowest 1 is quite a long time.

 

What you describe above is basically what we did on the said plumbers advice, you can also slow down flow rates in individual radiators.

 

If there's an adjustment on the op,s pump then it's a simple enough thing to try. The way the OP describes the problem though is exactly the same as when trying to get ours going, so my hunch is it will work.

[Ex- Member]

So you did not read my first 11 words, are you being deliberately argumentative? My caveat was there in my first answerer - where is yours?

 

Please now explain the physics behind your assertion that the pressure in the system can affect how rapidly the water warms up. I do not believe that you can because the rate of warm up is dependant upon the volume of water and the amount of heat being being supplied. Nothing to do with the pressure PROVIDING the system is full of water but even if it were not as long s the pump could circulate the water through the boiler the pressure will still not have an effect. The only thing the pressure will affect is the boiling point.

 

Now, as far as assisting the OP. Where did he tell you that he had a sealed heating system with a pressure vessel? Sending him looking for an "accumulator" that may well not be there is not so much help either.

 

Yes, if anyone suggest that it is safe for a stove that we have no knowledge off the full controls to run with a sealed system I will continue to warn of the danger. Especially when others suggest that it is safe and good practise.

 

Perhaps you can also explain how the pressure in a sealed system that is boiling will be contained.

 

I have not even mentioned the difficulty in refilling the sealed system with liquid containing anti-freeze unless you also buy a pump. That in itself would in my view suggest they are not best suited to boat use where DIY is far more common than at home.

 

I do concede though the the water temp does not rise quicker under pressure though, I recall getting this wrong in the last thread on this too.

[nicknorman]

Julynian, I don't doubt you are sincere in your views. As were those who proclaimed the earth to be flat for thousands of years! But the bottom line is that, within reason, the flow rate through a boiler has virtually no impact on heat transfer from said boiler. It can have some effect on heat distribution to various parts of a system, with one bit getting hotter at the expense of another bit being cooler.

[Ex- Member]

Julynian, I don't doubt you are sincere in your views. As were those who proclaimed the earth to be flat for thousands of years! But the bottom line is that, within reason, the flow rate through a boiler has virtually no impact on heat transfer from said boiler. It can have some effect on heat distribution to various parts of a system, with one bit getting hotter at the expense of another bit being cooler.

 

What can I say, It's not a view though, a slower flow heats the boat quicker than a faster one. Maybe heat is getting lost somewhere on a faster flow for some reason, or as you suggest we're feeling it quicker, but it makes a significant difference on this boat.

 

Is it possible on a fast flow that not all the water is going through the rads? as they maybe can't take that particular flow rate being produced so fluid stays in the lower pipework which in our case wouldn't directly heat the boat.

 

We do have a diversion that flows under the composting toilet to warm it which is under the floor, maybe water being forced through that pipe is cooling under the floor, but at a slower rate doesn't.