Back Boiler and pumped CH

[Theo]

Sorry that I am cluttering up your screens. Blackrose has discovered a really weird error and I am trying to find out what is wrong.

Nick

Edited September 29, 2012 by Theo

[Theo]

This is really Blackrose's topic. He encountered a very peculiar error which we have now worked around.

I've recently connected the backboiler of my solid fuel stove to a pumped central heating system. The stove also runs a thermocycling system but the backboiler thumps when it gets really hot and I've been told the two rads aren't getting rid of enough heat and the stytem is overheating.

 

I've recently connected the backboiler of my solid fuel stove to a pumped central heating system. The stove also runs a thermocycling system but the backboiler thumps when it gets really hot and I've been told the two rads aren't getting rid of enough heat and the stytem is overheating.

 

the backboiler has 4 ports, so I decided to kill two birds with one stone. I'd connect the blanked off ports to the pumped central heating system, which is indirectly via a heat exchanger, and get some free hot water in my calorifier too.connected to the engine.

 

I thought T-ing the flow and return of the CH system into the backboiler and running the pump would heat the system, but it doesn't work and the pipes between the stove and central heating system barely get warm! Should the pump be between the stove and central heating system?

 

I haven't labelled this diagram. The thermocycling system is in red and it works fine (apart from getting a bit too hot). I hope the rest is self-explanatory.

 

Edited September 29, 2012 by Theo

[smileypete]

What happens with the gravity rads when the pump is running, do they cool right down or remain hot?

 

cheers, Pete.

~smpt~

[blackrose]

What happens with the gravity rads when the pump is running, do they cool right down or remain hot?

 

cheers, Pete.

~smpt~

 

They remain hot.

 

Perhaps there was some sort of airlock in the pumped CH system when I tested it?

 

I'm just wondering whether the pump is forcing the water around the main flow and return pipes without going up the pipes connecting it to the stove? But then how does it force water into the rads? The stove is plumbed in with the same principal.

 

On a related side issue: I installed 2 full bore 22mm isolators on the pipes from the stove to the pumped CH system, just in case it didn't work or I wanted to work on it. I tried isolating the system but the coolant/antifreeze seems to be gradually getting past them! I know that antifreeze reduces the viscosity of water so I'm wondering if domestic plumbing isolators aren't designed for antifreeze?

 

http://www.toolstation.com/shop/Plumbing/Valves/Full+Bore+Isolating+Valve+CP+22mm/d20/sd2696/p64136

Edited September 29, 2012 by blackrose

[the grinch]

looking at your picture i see that the pump? is at the end of the pipe run if so it is definately in the wrong place for a 2 pipe system flow/return it would work on a 1 pipe (i:e) all flow through each radiator - no tees)

otherwise you will need to put the pump before the first rad or after the last return from a rad on the primaries at the moment all you will achieve is to circulate the water from pump to the nearest rad and back

 

also the left hand rad is piped up wrong as you have effectively piped both tails to the same pipe you would need to remove the pipe between the 2 rad tails

 

and the right hand red appears to have 2 returns?

[blackrose]

looking at your picture i see that the pump? is at the end of the pipe run if so it is definately in the wrong place for a 2 pipe system flow/return it would work on a 1 pipe (i:e) all flow through each radiator - no tees)

otherwise you will need to put the pump before the first rad or after the last return from a rad on the primaries at the moment all you will achieve is to circulate the water from pump to the nearest rad and back

 

Yes, that is the pump you're looking at (at the end of the line), but I don't quite understand? The system used to work from the eberspacher pump (in more or less the same place as the current pump, and it also works from the engine/heat exchanger system using the same pump as in the diagram.

Edited September 29, 2012 by blackrose

[the grinch]

again the right hand red doesn't need the extra pipework between flow tail and return tail

 

was the ebers pump a pump in the true sense or like central heating ones just a circulator? (i know nothing of their pumps)

 

the way you have shown it there is very little positive pressure just from pump to first rad and far to much negative pressure (the rest of the pipework and rads)

[smileypete]

Looking at it the pump should be in the return pipe to the backboiler, in the pipe run to the backboiler after it tees together from the pumped rads.

 

Also it looks like there is a loop between flow and return on the very left pumped rad which shouldn't be there.

 

Edit: Modified piccy:

 

 

The pump should go on the pipe that goes to the lower connection on the backboiler, and pump towards the back boiler.

 

cheers, Pete.

~smpt~

Edited September 29, 2012 by smileypete

[Theo]

looking at your picture i see that the pump? is at the end of the pipe run if so it is definately in the wrong place for a 2 pipe system flow/return it would work on a 1 pipe (i:e) all flow through each radiator - no tees)

otherwise you will need to put the pump before the first rad or after the last return from a rad on the primaries at the moment all you will achieve is to circulate the water from pump to the nearest rad and back

 

also the left hand rad is piped up wrong as you have effectively piped both tails to the same pipe you would need to remove the pipe between the 2 rad tails

 

and the right hand red appears to have 2 returns?

 

I rather think that there is a further problem with the connection at the left hand end of the blue run. ISTM that it will short the circulation through the radiators.

 

N

 

Looking at it the pump should be in the return pipe to the backboiler, in the pipe run to the backboiler after it tees together from the pumped rads.

 

Also it looks like there is a loop between flow and return on the very left pumped rad which shouldn't be there.

 

Edit: Modified piccy:

 

 

The pump should go on the pipe that goes to the lower connection on the backboiler, and pump towards the back boiler.

 

cheers, Pete.

~smpt~

 

Spot on!

 

N

 

 

[blackrose]

again the right hand red doesn't need the extra pipework between flow tail and return tail

Well that's the way it's always been and it works fine. I connected the final rad on that system that way to ensure good circulation without a pump. Anyway, the thermocycling system works fine and isn't the problem.

 

was the ebers pump a pump in the true sense or like central heating ones just a circulator? (i know nothing of their pumps)

I don't know - it was an eberspacher DW10. Probably just a circulation pump.

 

the way you have shown it there is very little positive pressure just from pump to first rad and far to much negative pressure (the rest of the pipework and rads)

I don't really understand what you mean? The diagram is just a schematic.

 

Looking at it the pump should be in the return pipe to the backboiler, in the pipe run to the backboiler after it tees together from the pumped rads.

 

Also it looks like there is a loop between flow and return on the very left pumped rad which shouldn't be there.

 

Edit: Modified piccy:

 

 

The pump should go on the pipe that goes to the lower connection on the backboiler, and pump towards the back boiler.

 

cheers, Pete.

~smpt~

 

Yes, that's what I was thinking. If I plumb it that way would I assume the coolant would still go around my heat exchanger so I could still heat the boat from the engine if I want (the heat exchanger is at the pump end of the system, but not shown in my original diagram.)

 

Thanks for the advice chaps. I will modify the system as soon as I can work out why those damn isolators aren't working! I put them in for just this eventuality, thinking that I could still run my stove & themocycling CH system while working on the pumped side of the CH system. I'd assumed that the screwdriver slot on the isolators showed open with the slot in-line with the fitting and closed with the slot at 90 deg to the fitting, but I'm not sure if they do?

Edited September 29, 2012 by blackrose

[the grinch]

Looking at it the pump should be in the return pipe to the backboiler, in the pipe run to the backboiler after it tees together from the pumped rads.

 

Also it looks like there is a loop between flow and return on the very left pumped rad which shouldn't be there.

 

Edit: Modified piccy:

 

 

The pump should go on the pipe that goes to the lower connection on the backboiler, and pump towards the back boiler.

 

cheers, Pete.

~smpt~

 

 

thats better the blue circuit should now run fine although you may need a small amount of restriction on the locksheild valve on the single rad section to balance it

 

still cant understand the 3 connections to the right hand red rad though?

[blackrose]

 

still cant understand the 3 connections to the right hand red rad though?

 

There are actually 4 connections to the last rad on the termnocycling system! When I built the system I was told that the final rad on a termocycling system should be fully connected because in some cases final rads on unpumped systems don't get hot. Anyway, it works well and they do say if it ain't broke.... so I won't be changing it.

[smileypete]

Yes, that's what I was thinking. If I plumb it that way would I assume the coolant would still go around my heat exchanger so I could still heat the boat from the engine if I want (the heat exchanger is at the pump end of the system, but not shown in my original diagram.)

Not ideal but it should be OK, maybe try it sometime and see. The diagram also misses out a header tank, feed and vent pipe on the gravity rad side of the boiler, which I hope is there!

 

Thanks for the advice chaps. I will modify the system as soon as I can work out why those damn isolators aren't working! I put them in for just this eventuality, thinking that I could still run my stove & themocycling CH system while working on the pumped side of the CH system. I'd assumed that the screwdriver slot on the isolators showed open with the slot in-line with the fitting and closed with the slot at 90 deg to the fitting, but I'm not sure if they do?

They should isolate with the slot perpendicular (across) the flow direction. How can you tell that flow is getting past them? Might be handy to have an isolator on the other side of the pump too.

 

cheers, Pete.

~smpt~

Edited September 29, 2012 by smileypete

[blackrose]

Not ideal but it should be OK, maybe try it sometime and see. The diagram also misses out a header tank, feed and vent pipe on the gravity rad side of the boiler, which I hope is there!

Yes, it's all there. The thermocycling system is self-bleeding as the header tank Ts off at the highest point of the top run.

 

They should isolate with the slot perpendicular (across) the flow direction. How can you tell that flow is getting past them?

Because the level in the header tank of the pumped system rises a few hours after I put water into the thermocycling system even though they are apparently isolated from each other. One or both of the isolators seems to be leaking.

[the grinch]

There are actually 4 connections to the last rad on the termnocycling system! When I built the system I was told that the final rad on a termocycling system should be fully connected because in some cases final rads on unpumped systems don't get hot. Anyway, it works well and they do say if it ain't broke.... so I won't be changing it.

 

your drawing shows only 3 that is why i questioned it as in 30+ years of plumbing i have never seen it 4 connections i understand!