Erratic central heating

[jtee]

Season greetings.

Wonder if somebody can help with the latest problem I have with my central heating please. It’s an open, pumped system with a Potterton e60 boiler.

The central heating boiler and pump won’t come on unless the hot water is switched on. If I leave the central heating on with the water it stops working erratically. I then need to turn both off for a while – i.e. 30 mins – then switch it back on for it to start working again. It almost seems as though either the water is getting too hot and switching off the boiler or too much pressure is building up.

I did change the fuse box which the thermostat, timer and pump connect to and although I thought I put the wires back in the same place it sounds as though something is not quite right.

Although it’s not the end of the world having both on at the same time why would the heating keep closing down?

Any help would be much appreciated. I have so far changed the pump, thermostat and two rads. I don’t know whether it’s got anything to do with it but one of the rads, the lowest and possibly last on the system has hot water running into it but does not follow out. I have tried bleeding the rad and total systems but nothing works. Thought about flushing but need to guarantee that would help as it's costly!

Could it be the thermostat which is approx. 15 years old (Honeywell e40)?

Thanks.

 

[Billy Bob Bob]

motorised valve failed

 

[Blake]

What state was the pump in when you changed it? Loads of sludge, black etc or ok?

Try turning off other rads completely on order to force the water around the radiator which is not working.

Do you have a 2/3 port valve in the cupboard with cylinder, if so, this may not be working correctly.

Check for frozen pipes on the system, as this can give the same symptoms as a blockage.

 

[jtee]

Thanks Bronzino,

There was a blockage above the pump on the return; the water was unable to complete the circuit so emptied in the expansion tank. I replaced the pipework and every seemed to be resolved. I also replaced to old rads which had black slime in them. I have only two old rads left on a 6 rad system. When I drain the water from the system is pretty clear but then there could still be a partial blockage somewhere. It's not frozen pipes. I have a couple of pictures which show the valve.