Gravity flow back boiler problem

reilig · 04-01-2010 11:05am #1

Just moved into the new house. Have a triple coil cylinder with central heating boiler and stanley range connected to it - other coil is for solar eventually.

The stanley range has a small boiler specifically for DHW and is on a gravity flow. We have only lit it once since we moved in and it seemed to continually blow water into the overflow tank when it heated up. Is it supposed to do this (every 10 minutes)?? The return pipe from the cylinder does not seem to get warm at all.

Any thoughts or solutions???

davidoco · 04-01-2010 2:24pm

Perhaps you already had a full tank of hot water when you lit the stanley.

Hot water from the stanley would normally travel up the flow pipe, get cooled by heat exchange in the cylinder and move back down thereby creating the gravity flow. If the cylinder water was already hot, the hot water rising had nowhere to go and blew out the overflow.

solution - fit a pump on the stanley.

blackbox · 04-01-2010 4:13pm

Davidoco,

if your theory was correct then the return pipe would be getting hot too - As long as the Stanley is hotter than the cylinder, the water should circulate (assuming the cylinder is actually above the Stanley!). The Stanley would have to be actually boiling the whole cylinder - this would be obvious from the temperature in the hot taps.

Reilig,

I suspect that there may be air in the Stanley circuit that has not been properly bled - as it expands it is bubbling up. There could be a problem with the feed to this circuit - can you trace it to ensure valve(s) are open.

A more serious possibility is that the return line is restricted or blocked. This would cause the water to boil in the circuit and bubble out the expansion tank. In this case you would probably hear it boiling at the Stanley. If so, you should put out the fire in the Stanley.

Micky Dolenz · 04-01-2010 5:32pm

sounds like an airlock alright. Once fixed and depending on how fast it heats the cylinder, it may be an idea to fit a rad in the hot press or attic etc as a heat dump.

ccsolar · 05-01-2010 1:32am

you should have a pump on the stanley and also if the return pipe is cold you might have an air lock which will need to be released.

CC

reilig · 05-01-2010 10:58am

Thanks guys. I suspect it might be an airlock. I will see what I can do to release it today.

The hot water cylinder is cold at the present time.

The cylinder is above the range and the pipes linking it have correct levels to allow the gravity flow.

There is no boiling at the range when the fire is lit.

I really don't think I will need a radiator as a dump for the heat. The DHW tank is 300 litre. It would take a roasting fire for several days, without using any hot water from the tank to fill it from top to bottom with hot water.

I thought the whole idea of a gravity flow was that you didn't need a pump?

I will let you know how I get on. Thanks for the advice.

Dan

Micky Dolenz · 06-01-2010 1:44am

your right, with a 300 L tank you probably won't need a heat dump.

under no circumstance should any valve or obstruction be fitted on a gravity circulation system, no pumps, no pump valves etc. Ensure that the flow rises from the stove and return is always falling, check for any unlevel sections of pipe work. Don't be afraid to loosed a joint, this may free out the air..

demanufactured · 06-01-2010 1:51am

one question OP...Why didnt you go for a duel fuel setup with the stanley heating the rads too...not being smart or anything just curious.

reilig · 06-01-2010 11:09am

demanufactured wrote: »

one question OP...Why didnt you go for a duel fuel setup with the stanley heating the rads too...not being smart or anything just curious.

I thought about it for a long time and got a lot of advice from my plumber about it. I have a log gasifying boiler in my garage and a Stanley Errigal range which has a very small fire box.
My reasons for not going with a duel fuel set up:
The gasifying boiler is 2x more efficient than a range. So it uses less fuel for more and constant heat.
A range to heat the radiators in my house would have cost over €5k, where as my small range cost just over €2k.
A larger range would be too hot for my kitchen.

But I suppose the main reason is the efficiency of the gasifying boiler. Why heat my house with a range when I can do it much more efficiently with the gasifying boiler - the wood is stacked beside the boiler and it makes no mess - whereas it would make a mess if I had to carry it into the house a number of times per day to keep the range filled. The plan is to light the boiler and range once per day. heat the house with the boiler. heat the hot water with the range and the o/h wants it for cooking. It also heats the kitchen nicely.

reilig · 07-01-2010 10:54am

Just a note to thank you all for your advice, especially CCSolar for his PMs.
Just to let you know that the problem has been resolved - well it will be resolved in the coming days. I got my plumber to look at it yesterday. He released some air from the system and it worked a little bit better. However, as CCSolar suggested, my plumber confirmed, we will have to install a small circulation pump on it as the gravity flow will not go through the coil in the cylinder properly. Luckily I have left wires for this purpose so its not a major inconvenience.

Thanks again for the advice guys!!!

GoOnTaigh · 25-10-2010 8:30pm

Please please help. I am having the exact same problem with an Erin Solid Fuel stove with back boiler connected to a 300L water tank with 3 coils.

When I light the fire the flow pipe gets red hot but the return pipe is stone cold. The flow is fitted with a thermo stat that kicks on a pump to the rad's, they dont get hot and the rad circuit is also cold but when the fire is lit I can hear the water boiling in the back bolier but it doesnt seem to be circulating at all.

Plumber opened nut on the flow and released some air, cured the problem for a day or two but then gets worse again. I cant keep opening nut's every day as its just not a proper solution. The pipe work to the tank has a number of bends due to location, but but not a long distance.

Can anyone advise on how to get this working properly? Anyone fit a pump on the flow and return coil? I suggested this to the plumber but his answer was that the water would circulate too quick and this wouldnt work.

I've read that it can be dangerous to fit a pump to the flow and return as if you light a fire, electircity goes off then the water cant circulate and could explode.

Thanks in advance

ccsolar · 25-10-2010 9:23pm

GoOnTaigh wrote: »

Please please help. I am having the exact same problem with an Erin Solid Fuel stove with back boiler connected to a 300L water tank with 3 coils.

When I light the fire the flow pipe gets red hot but the return pipe is stone cold. The flow is fitted with a thermo stat that kicks on a pump to the rad's, they dont get hot and the rad circuit is also cold but when the fire is lit I can hear the water boiling in the back bolier but it doesnt seem to be circulating at all.

Plumber opened nut on the flow and released some air, cured the problem for a day or two but then gets worse again. I cant keep opening nut's every day as its just not a proper solution. The pipe work to the tank has a number of bends due to location, but but not a long distance.

Can anyone advise on how to get this working properly? Anyone fit a pump on the flow and return coil? I suggested this to the plumber but his answer was that the water would circulate too quick and this wouldnt work.

I've read that it can be dangerous to fit a pump to the flow and return as if you light a fire, electircity goes off then the water cant circulate and could explode.

Thanks in advance

Hi
The flow from your stove must be rising or you will have this problem also the return to the stove must drop.
I would fit a small pump to solve this problem, but others may disagree.
Can you check that your pump and stat is working as there might be a problem there.

Cc

GoOnTaigh · 25-10-2010 9:40pm

Thanks ccSolar, the stat and pump are working. The flow pipe get's very hot, the stat is set to 65 Degree's on the Flow and is conected where close to where the flow enter's the tank. When the flow pipe get's to 65 degree's the pump for the rad's come's on as I can feel it running and it has a light on it. The water flowing around the rad circuit is luke warm at most on flow and return of rad circuit.

I suspect the gravity flow and return from the stove to the cyliner is not working properly. I think a pump on this would help but I'm curious to know if anyone else did this and what the thought?

Other post's I read state that the gravity flow and return should be free of all values, pumps etc. not sure what to do to fix it.

reilig · 26-10-2010 10:13am

GoOnTaigh wrote: »

I suspect the gravity flow and return from the stove to the cyliner is not working properly. I think a pump on this would help but I'm curious to know if anyone else did this and what the thought?

CCSolar is right and your suspects are correct. I ended up having to put a small pump on the run between my stove and my DHW cylinder - luckily my electrician was smart enough to leave a wire for it just in case. Taking the air out of it did help a little, but it still overflowed into the expansion tank. Its been running for a couple of months now and is great.

Other post's I read state that the gravity flow and return should be free of all values, pumps etc. not sure what to do to fix it.[/

A gravity flow and return should be free of all valves etc, but once you put a pump onto it, you are no longer relying on gravity to bring the hot water around the coil. The pump will do this for you.

GoOnTaigh · 26-10-2010 7:46pm

Hi Reilig

Thanks for the reply. I have another plumber coming to take a look later in the week.

I lit the fire again this evening. Can you tell me how long does it take for your rad pump to come on after you light the fire? More or less as soon as my fire is lit and heat's up the rad stat on the coil flow hit's 65 and kicks on the pump to the rads. When I put my hand on the rad flow it's cold or luke warm at best even though I can hear the water boiling away in the back boiler of the stove. I'm starting to think there is air in the stove boiler as well. How do you bleed this, I was thinking of when the stove is cold, activate the rad pump then loosen the nut's at the back of the stove in an attempt to bleed the back boiler.

I'm disappointed I've had so many problems with the stove, I know people who have them and are delighted with them. Mine is driving me cracked at this stage

Thanks again

Gravity flow back boiler problem

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