Boiler problem

[Nickle98]

My Father-in-Law has a gravity heating system which also works the DHW. On the boiler there is an option to work just the water or the water and heating together but not just the heating alone. When the heating is on the hot water cistern seems to 'over cook' and then hot water feeds back into the base of the header tank in the loft which then causes it to overflow. My first thoughts are that it could be the cistern has had its day or possibly the motorised valve is not working. I am a relative novice to the heating side of life and would appreciate any advice to enable us to narrow the problem down in order to change the 'correct' part.

 

[simond]

You have a pumping over scenario and it is not a matter of changing a part.

If you search for 'pumping over' you will find a wealth of info, mainly revolving around sludge, blocked pipes, pumps running on speed 3 and TRVs installed without thought of the consequences.

 

[Nickle98]

Hot water is definately coming back through the feed and expansion pipe into the expansion tank. Having read some of the information as you advised it seems I have a 'seesawing' problem. Would this be correct??? Many thanks

 

[Tipper]

Is there actually a circulating pump or do you mean it's a gravity/thermosyphon system with no pump?

 

[Nickle98]

There is definately a pump. We have turned the pump down to number 1 setting but the sound of water gushing through the pipe works and the overflow pipe hurtling hot water out of the house made us turn the heating off again. Some of the radiators are now cold and some hot. It's a day mare and it's pretty cold here. Any advice (apart from buy a warmer coat) will be very much appreciated. Regards, a very cold off duty soldier (it's warmer in Afghan!!!)