Coal Boiler overheats the cylinder

[Donmac70]

Hello all, i have a coal fired central heating system with grant hydrograte back boiler, recently i had to renew hot water cylinder and immersion stat to modern one,problem the stat keeps tripping as the coal fire is heating the water in the cylinder beyond the the stats cut off and you only find this out when you go to use the immersion heater , thanks

 

[JohnD]

I expect it is the Immersion Heater Overheat stat you are thinking of, not the Cylinder Stat

Do you have a bathroom radiator or towel rail to help use the excess heat?

There is a thing called a Cyltrol that you can use to stop gravity circulation to a cylinder once it is hot, but controlling circulation of a coal boiler is more complex as they can overheat badly if circulation is stopped. I have no recent experience of solid fuel boilers, but I expect someone else will be along in a minute

 

[Donmac70]

thanks john d, my brother is a plumber and my pal is a sparkie and iam a slater/ fireplace installer but between us we are struggling to come up with an answer apart from getting an old stat which seem hard to source ,there is 7 radiators and a heated towel rail run of the system

 

[JohnD]

is it a pumped system? maybe you could put a valve on the cylinder supply to divert the flow to a large radiator as a heat-sink when the cyl is up to temp? It will need more than a towel rail. but with solid fuel I understand you must always have an open pipe for the heat to escape. Does the solid-fuel boiler have a thermostat to damp down the fire? the big problem is preventing the boiler overheating if the heat has nowhere to go. Not my area.

 

[Donmac70]

thanks john d, its a fully pumped system, my brother is going to try turning down the temperature on the stat that is clamped onto the pipe on the outside of the cylinder, to bring on the pump at a lower temperature, only thing it will impact on the temperature of the hot water, any other suggestions apart from that ?

 

[JohnD]

turning down the cyl stat will make the pump turn off at a lower temp, not on, unless there is something unusual about your system design.

 

[kevplumb]

its normal john to have a pipe stat on solid fuel

starts the pump only when the boiler is heated

stops condedsation in the boiler

 

[Boilerman2]

Is your new cylinder Foam lagged? I'll bet the old one wasn't, Cut all of the lagging off the new tank to create some heat loss, we had to do this recently on a Cylinder connected to an AGA it was the only way we could stop the water boiling up!!

 

[Donmac70]

hello all ,do you think the plan to turn the temperature on the pipe stat for the pump to just below the temperature of the emmerser stat will stop it tripping without impacting too much on the hot water we get from the coal fire

 

[Donmac70]

i know for definite the new cylinder is insulated and i think the old one was but it wasn't a problem then as it had an old type emmerser stat on it that didn't have the modern overheat trip switch on it