Back boiler Failure

[rusty69]

6 minutes ago, MtB said:

 

Before doing this, there is another technique the OP might be able to try. Potentially quite messy but I've used it to clear air locks successfully on gravity systems with missing vents in important positions.

 

Securely attach a hose pipe to the low point system drain cock and attach the other end to a nice fast-flowing mains water tap. Open the drain cock then open the mains water tap for as long as you dare. The fast flow into the drain cock, through the system and out into the header tank 'sometimes' disturbs and shifts enough air to get the system circulating. Then any remaining air tends to dissolve into the passing water.

 

But not always!

Wow, that is clever. Question:is adding copious amounts of cold water to a potentially hot system an ok thing to do? Asking for a friend. 

[MtB]

2 minutes ago, DShK said:

 

Ooer.. I will have to see if I have a long enough hose for that (I have to use a water tap quite far from me as my marina hasn't fixed my broken one for months...) and if I can figure a way to turn the water off quickly without spraying water all over the inside of my boat!

 

I will see which one of these worries me less when decision time comes!

 

Or even just try it with your boat domestic water tap at the kitchen sink. The flow rate will still far exceed that of the natural convection and just might make the difference.

 

 

 

 

[DShK]

2 minutes ago, rusty69 said:

Wow, that is clever. Question:is adding copious amounts of cold water to a potentially hot system an ok thing to do? Asking for a friend. 

Probably something to do when cold I would think. I am damping the stove down now to drain the system anyway.

 

Just now, MtB said:

 

Or even just try it with your boat domestic water tap at the kitchen sink. The flow rate will still far exceed that of the natural convection and just might make the difference.

 

 

 

 

 

Hmm, no idea how I would attach a hose to the sink tap!

[MtB]

2 minutes ago, rusty69 said:

Wow, that is clever. Question:is adding copious amounts of cold water to a potentially hot system an ok thing to do? Asking for a friend. 

 

Only if potentially hot. Prolly best not to do it if actually hot.

[MtB]

4 minutes ago, DShK said:

Hmm, no idea how I would attach a hose to the sink tap!

 

Oh no, fallen at the last fence!!! 

 

 

[rusty69]

These really simple gravity systems are pretty complicated aren't they? Or maybe just trouble shooting poorly installed ones. Think I will get rid of mine and install a chinese diesel heater.

Edited December 17, 2022 by rusty69

[Tony Brooks]

Just had a thought, how about one of these in place of a bleed point in a 28mm T

 

https://www.wolseley.co.uk/product/center-compression-blanking-plug-28mm-p543445/

 

Just a compression blanking disc, loosen the nut and it should leak to allow air out. I think it could be drilled and tapped for a brass hexagon setscrew with a soft washer under the head to seal it - a near instant DIY bleed point.

 

Edited December 17, 2022 by Tony Brooks

[GUMPY]

7 minutes ago, DShK said:

Probably something to do when cold I would think. I am damping the stove down now to drain the system anyway.

 

 

Hmm, no idea how I would attach a hose to the sink tap!

There are such things as universal tap adapters, just push on and tighten

[DShK]

14 minutes ago, Tony Brooks said:

Just had a thought, how about one of these in place of a bleed point in a 28mm T

 

https://www.wolseley.co.uk/product/center-compression-blanking-plug-28mm-p543445/

 

Just a compression blanking disc, loosen the nut and it should leak to allow air out. I think it could be drilled and tapped for a brass hexagon setscrew with a soft washer under the head to seal it - a near instant DIY bleed point.

 

I did think about this, we are on the same wave length! I still would be worried that if I cut, rather than desoldered the existing elbow. I might not have enough pipe left to fit a compression joint. And there isn't enough space in the horizontal pipe for a couple, I think. I might do Tracy's method as a temp bodge and then do it this way when it's warm.

13 minutes ago, Loddon said:

There are such things as universal tap adapters, just push on and tighten

Nice, ill see if I can find one at the diy stores today!

 

 

I managed to break free of the ice so I am free floating again. I think I might load my bow up with coal and water and see if refilling it like that avoids an airlock.

[ditchcrawler]

12 hours ago, Tracy D'arth said:

BEngo is partially correct.  The single pipe system of connecting radiators is a bit old fashioned and inefficient. It has the advantage here that the calorifier has priority and will heat quicker than if you re-pipe the flows of the rads to the flow pipe. I would be happy leaving the pipework as it is.

 

Similarly in a domestic situation with a large boiler BEngo is correct about the expansion and vent pipes. But on a boat with a small boiler most are done with a single combined fill and vent pipe connected only to the base of the tank. Yours is slightly better having an over tank vent but it is not essential.

The advantage of a single bottom connection is that any venting steam discharges under water and condenses straight away instead of steaming your boat out.

I would be happy to leave yours as it is or remove the over tank vent pipe. I have installed dozens of boat systems this way.

 

Now to get to the root of your problem.

 

Have you put a small spirit level on the flow pipe all the way along between boiler and calorifier top connection/vent?

 

If you do, I am sure you will find that the attitude of the hull in the water is removing any positive rise in that pipe. In other words you have an air lock in the flow pipe somewhere.  Test the rise of the pipe, fix any high unvented parts, then load the bow to get more slope on the pipe. I bet it will work then.

 

It makes little difference whether the pipe rises steadily or goes up high first, its the difference in height between flow and return pipes that determines the gravity flow rate counterbalancing the pipe resistance. What is vital is that it does not have any high part that holds air preventing the gravity flow.

What about if the calorifier is already hot and trying to make the water flow in the other direction when you light the fire?

[MtB]

38 minutes ago, Loddon said:

There are such things as universal tap adapters, just push on and tighten

 

But do we know if the OP has a universal tap? 

 

 

[DShK]

So, an update.

 

I had to seal a couple of weeping joints and let that dry. Since then I have ballasted the bow with about 300kg of extra weight, plus 400 litres of water total. I drained the system and refilled when I was free of the ice. No change.

 

I have got myself a tap adaptor and as suggested by MtB, pushed water into the system at the drain point at 1). Some gurgling occurred. The system felt a bit better that night - the lower pipe was warm (I isolated the rads) and the hot water was pretty hot. But the boiling continued.

 

Today, I notice that the header tank is much lower. The water does not really boil off here as far as I have noticed, but I do not see any leaks. I figured that perhaps some water found its way into a void and perhaps it would be better today. Perhaps there is a chance the coil is broken as previously suggested and this water is leaking into the calorifier tank? (health hazard!) I decided to try and push more water through from the tap, through the drain point at 7. No water would go in. I filled the header tank from 1), and tested to see if water would drain from 7). Nothing. I do not know if the drain point itself is blocked or this is indicative of the problem. I have held off drilling the speculative hole for now, as I am going back to my hometown for a week over xmas. I tried running the stove, and it boiled worse than yesterday.

 

Does this new info give any more insight? To be honest, this problem has eroded my mental health a bit. If I can't get this sorted out soon, I would like to get professional help. I am just not sure who I would speak to with regards to such a system - it doesn't seem like a job for a "normal" plumber. 

 

EDIT: As a thought, is it possible the ball valve (6) is not working correctly perhaps?

EDIT2: Forgot to mention, but I noticed rather than fall back to the stove, the lower pipe at (1) rises to the boiler a fair amount, even with the bow ballasted. Not sure if this makes much difference, thought I'd note it. Hard for me to change without redoing the whole lower pipe.

 

Edited December 21, 2022 by DShK

[rusty69]

1 hour ago, DShK said:

To be honest, this problem has eroded my mental health a bit. If I can't get this sorted out soon, I would like to get professional help.

OMG, its not so bad you need to see a psychiatrist, shirley?

 

But joking aside, and I may have asked this question before, but have you asked the previous owners if the system ever worked properly? 

[DShK]

5 minutes ago, rusty69 said:

OMG, its not so bad you need to see a psychiatrist, shirley?

 

But joking aside, and I may have asked this question before, but have you asked the previous owners if the system ever worked properly? 

I haven't, I think you're right, it might be time to do that. 

[rusty69]

36 minutes ago, DShK said:

I haven't, I think you're right, it might be time to do that. 

Well, at least if you can find out if it ever did work, then it's likely to be an air lock issue, or less likely a split coil.

 

If it didn't work, then you can decide to either re-work the pipework, or add a circulation pump.

Edited December 21, 2022 by rusty69

[MtB]

13 minutes ago, rusty69 said:

Well, at least if you can find out if it ever did work, then it's likely to be an air lock issue, or less likely a split coil.

 

If it didn't work, then you can decide to either re-work the pipework, or add a circulation pump.

 

There is a complication that can arise here. The Seller of the boat may be reluctant to admit the heating never works. There is no downside and potentially a lot of upside to them fibbing and saying 'Well it was working ok when I put it on the market".

[rusty69]

2 minutes ago, MtB said:

 

There is a complication that can arise here. The Seller of the boat may be reluctant to admit the heating never works. There is no downside and potentially a lot of upside to them fibbing and saying 'Well it was working ok when I put it on the market".

True, I suppose. But on the upside, there is a chance they may say it never worked properly. Lots to gain by asking, little to lose.

[MtB]

3 minutes ago, rusty69 said:

True, I suppose. But on the upside, there is a chance they may say it never worked properly. Lots to gain by asking, little to lose.

 

Yes agreed. No harm in asking now the OP is aware a claim it used work fine cannot necessarily 100% be trusted.

 

 

Edited December 21, 2022 by MtB

[DShK]

I would phrase it as "did you ever have issues with X and Y with the heating", rather than "did this ever work?!" They offered for me to contact them with any questions if I needed. Everyone around here seems to know them (to the point I sometimes feel like I'm living in someone else's boat!) So I don't think they will be underhanded.

 

When I asked them about my batteries gassing, they said they had the issue sometimes but just increased ventilation, for example.

I also had an idea - the ball valve is a compression fitting. If I remove that I can see if it works, and also if removing it allows me to push water through the nearby drain point

[BEngo]

As configured, the system is never going to prevent boiling in the back boiler when anything larger than a small  fire is going.  Even if the system is completely purged of airlocks, and the boat trimmed to a certain rise in the flow side, the thermal capacity of the  calorifier and its internal coil is wholly inadequate to absorb for very long the output of the back boiler (somewhere in the region of 2-5 kW, depending on the rate of firing in the stove).  As configured, the radiators can do nothing to dissipate  the heat, as there is no reason for any  hot water to pass through them. They are not even in a classic single-pipe configuration.  The set up is such that the  easiest route back to the boiler is all along the bottom pipe, which bypasses the rads.  Once the system starts to boil it will eject water, and steam,  from the flow pipe, thereby destroying the already limited thermal circulation and making things worse.

 

The way ahead is to reconfigure the radiator feeds so that hot water enters at the top and cooler water leaves at the base of each radiator.  Physics will then cause water to flow through them  dissipating the heat from the boiler.  Once circulation is going properly,  balance the flows so that the calorifier gets as hot as is needed.

 

N

 

 

[ditchcrawler]

1 minute ago, BEngo said:

As configured, the system is never going to prevent boiling in the back boiler when anything larger than a small  fire is going.  Even if the system is completely purged of airlocks, and the boat trimmed to a certain rise in the flow side, the thermal capacity of the  calorifier and its internal coil is wholly inadequate to absorb for very long the output of the back boiler (somewhere in the region of 2-5 kW, depending on the rate of firing in the stove).  As configured, the radiators can do nothing to dissipate  the heat, as there is no reason for any  hot water to pass through them. They are not even in a classic single-pipe configuration.  The set up is such that the  easiest route back to the boiler is all along the bottom pipe, which bypasses the rads.  Once the system starts to boil it will eject water, and steam,  from the flow pipe, thereby destroying the already limited thermal circulation and making things worse.

 

The way ahead is to reconfigure the radiator feeds so that hot water enters at the top and cooler water leaves at the base of each radiator.  Physics will then cause water to flow through them  dissipating the heat from the boiler.  Once circulation is going properly,  balance the flows so that the calorifier gets as hot as is needed.

 

N

 

 

But he is not even getting hot water back to the boiler, only warm so he is not getting the flow round the system. IMO and I am not a heating engineer, if his calorifier is hot with the stove off it will try to circulate water in the other direction, the boiler in the back of the stove will have to overcome this to get going. As i said I could be completely wrong on that point.

[BEngo]

1 hour ago, ditchcrawler said:

But he is not even getting hot water back to the boiler, only warm so he is not getting the flow round the system. IMO and I am not a heating engineer, if his calorifier is hot with the stove off it will try to circulate water in the other direction, the boiler in the back of the stove will have to overcome this to get going. As i said I could be completely wrong on that point.

Your feeling about reverse flow caused by the hot stored water in the calorifier is right, (subject to the vagaries of the pipework.)  There are several threads on here about the analogous situation where engines are kept warm overnight via  reverse flow by calorifier driven circulation and about the right sort of non return valve to prevent it.

 

If hot water is getting to the inlet of the cauliflower then, initially, warm water is what to expect at the outlet.  As the stored water heats so the outlet temperature will rise. When the cal reaches the same temperature as the inlet water, heat transfer will stop.  Circulation can continue  *IF* the rest of the system provides enough thermal drive to keep the water moving.

 

I agree his present  circulation through the calorifier and/or the rads is, at best, piss poor. I was addressing how to prevent the back boiler boiling and making the circulation worse. There are (or should be)  two driving forces at work: The lowering of water density in the boiler as the watter is heated. This causes the water to rise and push water ahead of it into the radiators.  The increasing density of the water in the radiators and calorifier as the water is cooled.This pushes water from the rads  into the return  pipe.

 

The first is working.  The second is not. 

Get the second working and there should be enough thermosyphon to get the water going through the cal as well.

N

[DShK]

This makes sense. I'm still not sure why I can't get any water in or out of that drain point I mentioned though, that still concerns me. But my understanding is, even if there is a blockage there, the rest of the system should function. Which will be an improvement! If the water does not get hot enough but the rads then do, I know there is something wrong in those bits of the pipe. Rather than drilling random holes in hopes to find an airlock I can't purge (for now at least!), I will reconfig the radiators when I am back on the boat. It should be fairly easy to do given I can find the right radiator bit.

 

Thanks again.

 

EDIT: Radiator valves seem to always be designed with the pipework coming from the bottom - I'm assuming I just want a straight pipe, so just flipping my valve upside down is the best way to go?

Edited December 21, 2022 by DShK

[Tony Brooks]

How a\bout  a horizontal one: https://www.screwfix.com/p/white-straight-manual-radiator-valve-15mm-x-1-2-/20141

 

Not so easy if you have to use the existing Ts of the feed or return pipe.

[BEngo]

I suspect that the washer in the drain plug has come off the piece that you turn and is stuck to the seat. To check this keep undoing the drain plug till it comes out.  Have old towel and a  bucket handy.  If there is a washer on the plug, but no water you have a blockage.  Clear it with a straightened wife coat hanger poked in where the screw plug came out

If there is a thin stream of water and no washer, ferkle the washer out with a small screwdriver or bent wire.  Then you should get plenty water.

Have a bucket or 4l ice cream tub handy.  But a new drain plug washer when you have the old one to size it.  There are two types- Type A and Type B.

 

You dont need new rad valves.  Rotate the upper one of the existing ones so the inlet points up  and fit a 28x28 x (size to suit shortened existing pipe)Tee in the top pipe. Obvs, blank off the now redundant lower Tees - a compression blanking cap is probably easiest.

N