Hello I hope somebody can help. Our oil fired central heating isn't working properly. Boiler fires up and runs briefly but seems to be in good working order (serviced in March and has been run all summer on hot water only) DH has changed the limit stat and water stat on the boiler and also changed the pump but we are only getting some heat upstairs. Could there be an electrical fault in as much as the pump is not starting? We used to hear the pump start to pump the water around the system but now there is no noise. Room stat maybe although that still 'clicks'? Control panel which is on the boiler (7 years old)
Turn the stat up so the pump should be running then hit the pump with a series of increasingly severe blows until it starts. A large spanner is the usual tool.
Could well be the pump, however it makes sense to diagnose this in stages eliminating each possible problem as you go...
There is a check list here:
formatting link
(really we need to know a bit more about the system to give accurate guidance).
If I assume for a moment its a Y plan setup like this:
formatting link
you can do basic diagnosis with a multimeter. You can make measurements either at a wiring centre if you have one, or at the devices in question.
If you find your wiring centre, it may have connections like:
formatting link
task would be to check the CH on output (pin 4 on the diagram) from the programmer is live when the programmer has heating "on". If not, the programmer (or cabling between it and the wiring centre) is faulty.
Next check the call for heat from the room stat (pin 5) goes live when you here the stat click as you turn it up. If it does not turn on and off in response to winding the stat up and down then the stat is faulty.
Turn the cylinder stat right down and the room stat up. This should cause the valve to move to the heating only position, and the orange wire should go live. This should cause the boiler to start and the pump to run.
(If the boiler starts but then shuts down it may indicate the pump is not running, and its tripping on an over temperature).
Check the supply to the pump goes live. If you think it is not turning then it may have a large screw cap in the middle of the front face. Remove this (have a cloth handy - some water may dribble out). Under it you should see the end of the shaft the impeller is mounted on. This should have a slot on the end that you can turn with a large screwdriver to free it if it has stuck).
If the pump is spinning, it could be it has broken in a way that means its not pumping properly, or it could be a fault at the boiler.
If you are sure its pumping, then check the call for heat at the boiler. If that stays live but the boiler goes out then it suggests either a boiler overheat or a fault of some sort (either its thermostat, or possibly its gas valve)
Does it still heat the hot water ok? If so, the pump is likely to be ok, but the boiler and pump are not being told to fire in heating mode.
It's a good idea to carry out the diagnostic tests suggested by John Rumm, but I would put my money on the problem being due to a faulty motorised valve.
Or just undo the silver cap and insert a screwdriver, locate on the end of the pump shaft and check it rotates fairly freely. A bit of water will dribble out but not a great deal, an old towel will cope. Best do this before the system is at operating temperature...
Spose its also worth noting that its possible that the system has convected circulation (aka gravity circulation) for the hot water, and the pump is only used for the heating...
Make & model of boiler, plus details of any valves etc would help.
True, but with a boiler only 7 years old, I had assumed that it was a fully pumped system. Also, with a gravity HW and pumped CH system, the boiler would usually still run in CH mode[1] even if the pump failed.
[1] Maybe not if it's a C-Plan - would need to think about that! Like you say, we need to know more about the system.
Thank you to everyone who posted with suggestions on how to fix our central heating problem. It was the pump after all but seemingly just a bit of unknown 'crud' which seemed to have caused it not to work. DH loosened the screw at the front, allowed some water to flow and now it's ok!
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.