My central heating system blew a fuse this morning. After I had replaced it, I found that the boiler worked fine and it heats the hot water tank perfectly. However, when the room thermostat calls for heat, nothing happens. I've checked the room thermostat and it is fine, the switch to turn on the room central heating also works fine. Any ideas as to why the heating doesn't come on? David
Thanks "ripped off"! The pump works fine when the water needs to be heated. When the rooms need to be heated, there is no sign of life in the pump. If it was the diverter valve, the pump would still be pumping wouldn't it? David
What boiler have you got. If its a combi some dont have pumps on the hot water relying on mains pressure larger units have 2 pumps. Is there a cct diagram on the back plate or cover?
Ok, let me have a go. the pump is knackerd. your H/W is hot because of the gravity of hot water. H/W rises and cold falls keeping the cerculation going on the H/W side. But not the rads as they will not flow without the pump running HOWS THAT?????
Yes, there is a programmer in the airing cupboard separate from the boiler. I tested the switching function on that. It is OK. The boiler is not a combi. It's a 20 year old Glow-Worm. There's only one pump. Unfortunately there is no cct diagram. The wiring looks a bit of a cowboy job. A yellow/green wire is used as wiring to the switch in the programer! (but it's been that way for 20 years presumably)
I don't think it is the pump. I can hear the pump pumping when the water is being heated. When the radiators need to be heated, there is no sound from the pump.
David, Dose the orange conductor on the valve come live when you move the manual override arm on the side of the valve?
David, It all begins with the 'Controller' switching a 'Live' to the Room Stat (Central Heating (CH)) and/or the Tank Stat (Domestic Hot Water (DHW)). If the Stat is closed (indicating a DEMAND) then this 'Live' is passed to the ZONE VALVE(S) which provides the supply to the motor winding and drives the valve open and at the end of its travel it closes a microswitch that then passes the 'Live' to the Pump and Boiler. If the CH isn't working then there is a problem with this sequence - the likely contenders are: burnt out Zone Valve motor coil and possibly the Zone Valve microswitch. You should be able to hear the action of the zone valve(s) when you switch the CH/DHW 'On'. A cheapo neon screwdriver is a very useful tool for chasing the lives around the system and a Wiring Management System allows you to fault find from the airing cupboard.
David, Dose the orange conductor on the valve come live when you move the manual override arm on the side of the valve? Rewireking, the microswitch is not activated by the manual overide lever however there should be a permanent Live on the orange wire (common).
Eye, you said "the microswitch is not activated by the manual overide lever". This is not correct. When you move the manual override you can hear the synchronous motor being forced round and the switches clicking as they operate. BB
Rewireking: The orange wire does not become live when I manually move the lever across. It only becomes live when the hot water thermostat calls for heat.
Eye Squared R: That's very helpful thanks. I Haven't located the problem yet, but you've told me how to look for it. David
> Steve: Sorry, I've no idea if my system is "S" plan or "Y" plan. Have a decko here then and see if you can work it out!
Rewireking: correction, if I move the lever absolutely as far as it will go and wiggle it, then the orange wire does become live. I guess that indicates a fault in the diverter valve?