Worcester 240 central heating keeps turning off

[jonnieboy]

My Worcester 240 combi boiler has just started cycling on/off more quickly than normal when the central heating is on. It fires up for just a few 10's of secs (occasionally minutes) at a time. Sometimes the rads get as hot as normal but generally they stay cool. I can hear a relay switching on/off as the heating cycles on/off and at times this is clicking every second on so.

The hot water is fine - I can run a bath and it stays fired up the whole time the tap is on.


Something in the exhaust (correct term?!) of my Worcester 240 combi boiler is knocking when the wind blows. I've taken the pressure cover off and spun the outlet fan and it isn't that. It sounds like a loose flap of similar.

Any ideas? Thanks in advance,

Jon
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[ChrisR]

Well the Central Heating temperature sensor/thermostat would be an obvious place to start, but I would expect the boiler to have time delay between firings - usually about 4 minutes. That would be a pcb function.
Generally, shorter bursts of on-time might point to circulation difficulties - worn pump or more likely, sludge-build up.

The xhaust pipe clearly needs looking at. That could cause problems if the air flow is affected; if the fan pressure sensor is getting interfered with it could well result in the sort of symptom you have. Corgi time really.

 

[jonnieboy]

Thanks for the advice. It is the CH temperature sensor that is faulty - I've measured the resistance as the water heats up and when it gets to a certain temperature it goes virtually open-circuit (and then recovers as the temp falls).

Replacing it looks straightforward enough but I assume the sensor is actually in the water flow so I need to drain the system. Is this just a case of draining it from a rad or is it more complex (or simple!) than that?!

Thanks again,

Jon

 

[croydoncorgi]

If you're sure it's the sensor, then isolate just the boiler and drain that only.