Boiler constantly firing up

Dick_here

Our boiler is kicking in almost constantly, even when there is no demand for water/heating.  Is it a 'simple' switch that has got stuck or is it likely to be a bigger issue potentially ?  Obviously it's working, which is the key thing, but working too well if you like, and it can't be doing it (or our bills) any good presumably.  It happened occasionally previously, but managed to right itself the next day at least, but no sign of it happening this time.  Any advice appreciated.  Thanks !

rob7475

Is it a combi boiler? How long does it fire up for and how often? Many boilers keep a small amount of water constantly hot to deliver hot water to the outlet quicker. This feature can usually be disabled though.

Dick_here

rob7475 said:

Is it a combi boiler? How long does it fire up for and how often? Many boilers keep a small amount of water constantly hot to deliver hot water to the outlet quicker. This feature can usually be disabled though.

Thanks, not a combi boiler, no.  It doesn't fire up for long, but that's partly because I've dialled down the water temperature so it doesn't last very long.  I've not measured how often but very regularly.

Bendy_House

A LOT more info needed, !!!!!!.
Make and model and age of boiler. A note of what the current control settings are  A list - ideally with photos - of ALL the boiler and CH controls.

Rodders53

Most likely imho is a stuck 'call for heat' microswitch in a motorised heating valve.  Possibly a mechanical stick but sometimes the contacts weld closed.

Water will be circulating in a bypass loop or if a vented system up to the header tank.

New head required unless you have the skills to dismantle and identify the part to replace.  Some heads are easily removed from the valve, others are screwed in place.  Either will require electrical connections to be dis- and re-connected with the power off, of course.  If not competent don't attempt it.

Manual operation of the valves may nudge the microswitch and cure it - or more likely not - but eventually some parts will need replacing.

Bendy_House

Following on from Rodders' post, if you can ID the motorised valves, then you should get a good idea by listening to them operate when the CH and DHW are turned on and off at their controls. Each valve should make a smooth whirrrrring sound ending with an audible 'click'. When turned off, the click should come first, followed by the whirrrrrtt.