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Back boiler Failure


DShK

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10 hours ago, DShK said:

After some research I have concluded that what I hear with the trickling is something called "waterfall flow" and is indeed caused by the build up of air. I will fit a manual bleed point and if it returns as an issue I'll fit an automatic bottle vent.

Depending exactly where it is in relation to the pump suction and pipe restrictions it may be under a slight vacuum when the pump runs and the auto bleed would let air in, not out. That is why I suggested the header tank as if you have an open vent and its on the suction side again you could draw air in. A boat system has very little head of pressure on it unlike a house with a header tank in the loft .

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4 minutes ago, ditchcrawler said:

Depending exactly where it is in relation to the pump suction and pipe restrictions it may be under a slight vacuum when the pump runs and the auto bleed would let air in, not out. That is why I suggested the header tank as if you have an open vent and its on the suction side again you could draw air in. A boat system has very little head of pressure on it unlike a house with a header tank in the loft .

This makes sense. I did try and block the header tank/vent up as much as I could (difficult due to the setup), didn't make a difference but perhaps it wouldn't if there is already air in the system. It sounds like moving the pump more towards the stove might help? I'll see how the manual bleed goes anyway

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3 hours ago, DShK said:

This makes sense. I did try and block the header tank/vent up as much as I could (difficult due to the setup), didn't make a difference but perhaps it wouldn't if there is already air in the system. It sounds like moving the pump more towards the stove might help? I'll see how the manual bleed goes anyway

You may be OK once that air is out and its sealed again. I have a radiator in the house that gathers air/gas, I have to make sure the pump doesn't come on while bleeding or it sucks 

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Okay I fit the manual bleed point. Same issue 🙃I guess I'll try and fit it closer to the stove next. Hopefully it'll fit behind my washing machine, I can use the cables for the old fridge and it'll not look ugly as sin.

 

I would like a win at some point!

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52 minutes ago, Tracy D'arth said:

Don't guess where to put the bleed point, use a spirit level to find the high point where the air will be trapped as I suggested weeks ago and you ignored.

I didn't ignore it. There are definitely some *gentle* slopes in the wrong direction in the bottom long length of pipe. One part leads to the backboiler itself, so air should end up venting. Other parts should end up in the rads. The top pipe is one long pipe which has no way to have high points - except the bit I put a bleed point, which is definitely a high point, and is a sharp bend so made the most logical sense to be the problem. If you watch the timestamped bit in this video, this looks to be exactly what I am hearing, and it's demoed in a sharp bend downward, which is what I have. Do tell me if this sounds wrong though.

 

I suspect this is where air is getting trapped, but I have a continual source of air building up there. I can't imagine that any small weeping I have in the fittings would be enough to create this. So I am thinking perhaps ditchcrawler is right, and air is getting drawn in from the vent/header tank.

 

 

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The only time i have heard whooshing sounds in a system on a boat it turned out to be hot water trying to do what it does best i.e. rise and being forced to go the wrong way. I suspect the system might not rise all the way to the end where the header tank is and then fall all the way back and the pump can't quite manage. Solution might well be to borrow some heavy stuff, sit it right on the front of the boat to trim it more level and then try it.

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10 minutes ago, Bee said:

The only time i have heard whooshing sounds in a system on a boat it turned out to be hot water trying to do what it does best i.e. rise and being forced to go the wrong way. I suspect the system might not rise all the way to the end where the header tank is and then fall all the way back and the pump can't quite manage. Solution might well be to borrow some heavy stuff, sit it right on the front of the boat to trim it more level and then try it.

 

I think the OP has the stove at the front of the boat, so a typical fore-aft trim is very likely to have the top pipe sloping the wrong way for gravity circulation, unless he has fitted the pipe with a counter slope relative to the floor to counteract the boat trim. Ditto the bottom pipe. Unless I could inspect the boat I can't add anything more apart from when our back boiler at home cracked, the early symptom was air/gas build up in the rads.

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13 minutes ago, Bee said:

The only time i have heard whooshing sounds in a system on a boat it turned out to be hot water trying to do what it does best i.e. rise and being forced to go the wrong way. I suspect the system might not rise all the way to the end where the header tank is and then fall all the way back and the pump can't quite manage. Solution might well be to borrow some heavy stuff, sit it right on the front of the boat to trim it more level and then try it.

I know the thermosyphon effect in this system does work much better when the boat is trimmed more bow down. It stopped behaving so well when I filled up the diesel tank. The noise happens whether the system is hot or cold though, and no matter the pump speed - it should be a decently powerful pump, it is designed for these kind of systems.

6 minutes ago, Tony Brooks said:

 

I think the OP has the stove at the front of the boat, so a typical fore-aft trim is very likely to have the top pipe sloping the wrong way for gravity circulation, unless he has fitted the pipe with a counter slope relative to the floor to counteract the boat trim. Ditto the bottom pipe. Unless I could inspect the boat I can't add anything more apart from when our back boiler at home cracked, the early symptom was air/gas build up in the rads.

That is concerning. I noticed a lot of water/staining out of my chimney again, I had actually considered if my old backboiler had not actually broken. I wondered if the water I was seeing was from the smokeless fuel - it does seem quite wet. Worried another boiler has broken now! Was the air build up quite slow though? When I bled the air, it seemed to be a problem again almost immediately. It feels like there would need to be a substantial leak for there to be air sucked in that way, that quickly?

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5 minutes ago, DShK said:

I know the thermosyphon effect in this system does work much better when the boat is trimmed more bow down. It stopped behaving so well when I filled up the diesel tank. The noise happens whether the system is hot or cold though, and no matter the pump speed - it should be a decently powerful pump, it is designed for these kind of systems.

 

Maybe it is too powerful, domestic central heating pumps often have/had a flow adjustment.

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31 minutes ago, Tony Brooks said:

 

Maybe it is too powerful, domestic central heating pumps often have/had a flow adjustment.

It is adjustable and I've got it on the lowest setting. This pump is also used in computer watercooling systems, which obviously are much smaller - it seems to be used in a range of systems

 

"Areas of application are circulating systems in industrial or medical applications, computer and laser cooling, hot water heating in a mobile home, weekend home or boat with battery or solar powered pump, ponds and aquariums, domestic hot water systems and car heaters."

 

Perhaps it would do better with even less flow, after all the thermosyphon effect would be fairly gentle? Perhaps if it is drawing air through the vent/header tank, it wouldn't if it was running more gently.

 

I guess I can try manually dropping the voltage by using thinner cables or putting another load in series with it? Not sure what load I would use. Perhaps a resistor?

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29 minutes ago, DShK said:

That is concerning. I noticed a lot of water/staining out of my chimney again, I had actually considered if my old backboiler had not actually broken. I wondered if the water I was seeing was from the smokeless fuel - it does seem quite wet. Worried another boiler has broken now! Was the air build up quite slow though? When I bled the air, it seemed to be a problem again almost immediately. It feels like there would need to be a substantial leak for there to be air sucked in that way, that quickly?

 

First of all the staining could be from wet fuel or condensation forming when hot flue gasses hit cold chimney surfaces and running down.

 

I just gave the sypmtom of my house cracked back boiler. It was only in the spring, with small intermittent fires, did I find damp ash in the stove. However, that was a cast iron back boiler. This was over 40 years ago and I don't remember how fast the air built up.  I am certainly not saying your boiler is cracked.

 

Your noise could be caused by "turbulent flow", rather than "laminar flow" in the pipework. Your talk of a sharp bend suggest an elbow rather than a long (street?) bend, and any elbows are likely to cause turbulent flow, especially at higher flow rates.

 

 

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12 minutes ago, DShK said:

 

 

I guess I can try manually dropping the voltage by using thinner cables or putting another load in series with it? Not sure what load I would use. Perhaps a resistor?

I would use a PWM controller to drop the speed and infinitely adjustable 

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22 minutes ago, DShK said:

It is adjustable and I've got it on the lowest setting. This pump is also used in computer watercooling systems, which obviously are much smaller - it seems to be used in a range of systems

 

"Areas of application are circulating systems in industrial or medical applications, computer and laser cooling, hot water heating in a mobile home, weekend home or boat with battery or solar powered pump, ponds and aquariums, domestic hot water systems and car heaters."

 

Perhaps it would do better with even less flow, after all the thermosyphon effect would be fairly gentle? Perhaps if it is drawing air through the vent/header tank, it wouldn't if it was running more gently.

 

I guess I can try manually dropping the voltage by using thinner cables or putting another load in series with it? Not sure what load I would use. Perhaps a resistor?

Have you tried it on the highest setting when the fire is at its maximum? I’ve got the same pump connected to a reflex stove. The pump had to be switched on all the time. Put a temp sensor on the flow to make the pump modulate. Took temp reading of the flow and return to try and get the sweet spot . A lot of faffing about with the temp setting and pump speed finally got it to work ok. Before that you got a lot of whooshing and banging before the pump would move the water around. I can still override the sensor and just leave the pump running when the fire is a light like it was before without any problems. I also have a air vent in the pipe work next to the boiler which is the next highest vent point apart from the header tank.

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22 minutes ago, Jon57 said:

Have you tried it on the highest setting when the fire is at its maximum? I’ve got the same pump connected to a reflex stove. The pump had to be switched on all the time. 

If you have to have a pump that is the best way in my opinion. the very hot back boiler doesn't keep getting hit with cold water until the system warms up.

 

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On 13/03/2023 at 10:19, ditchcrawler said:

I would use a PWM controller to drop the speed and infinitely adjustable 

So I did this, and with the pump set to where it will only just start running, it works pretty well. Not perfect mind you, air does find it's way to the high point again, and then it does need bleeding otherwise it makes a huge fuss again. So far I've usually needed to  do this in the morning and maybe once during the day. Not perfect, but I reckon if in due time I move the pump down away from the header tank, it'll work great. So thanks for the great idea! I have a heating system which doesn't drive me insane again. Thank you!

 

On 13/03/2023 at 10:43, Jon57 said:

Have you tried it on the highest setting when the fire is at its maximum? I’ve got the same pump connected to a reflex stove. The pump had to be switched on all the time. Put a temp sensor on the flow to make the pump modulate. Took temp reading of the flow and return to try and get the sweet spot . A lot of faffing about with the temp setting and pump speed finally got it to work ok. Before that you got a lot of whooshing and banging before the pump would move the water around. I can still override the sensor and just leave the pump running when the fire is a light like it was before without any problems. I also have a air vent in the pipe work next to the boiler which is the next highest vent point apart from the header tank.

It made those noises without the stove alight.

 

On 13/03/2023 at 11:07, ditchcrawler said:

If you have to have a pump that is the best way in my opinion. the very hot back boiler doesn't keep getting hit with cold water until the system warms up.

 

The problem with this system, I've noticed. Is that the hot water is luke warm in the morning. When the fire goes out during the night, it keeps circulating the water and saps heat from the calorifier. I guess it's just something to live with.

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15 hours ago, DShK said:

that the hot water is luke warm in the morning. When the fire goes out during the night, it keeps circulating the water and saps heat from the calorifier. I guess it's just something to live with.

Put a pipe stat on the outlet of the stove, arranged so that it switches the power to the pump off when the pipe cools down.  

 

N

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