Oil fired boiler running constantly

[Graeme]

We have a conventional oil fired HW/CH system, floor standing boiler ground floor, HW tank first floor and cold water tank in the loft. The system is divided into four zones (three CH and one HW) and I noticed this morning that the boiler was running with all four timers off.

No wall stats, just stats on each radiator. One pump and motorised valves.

Removed the four timers from the wall - no change.

Changed the Honeywell control box on the boiler - no change.

The only ways to stop the boiler running are turn down the thermostat on the boiler or remove the Honeywell control box or turn off the power to the boiler.

Any thoughts on how the boiler can run without any of the timers being on?

[Graeme]

In message [e-mail]>, Graeme [e-mail]> writes

UPDATE

Just noticed that, when fiddling with the three motorised valves, and moving the little lever, two levers met the usual resistance, but the third didn't so disconnected the third one and problem solved. Luckily the valves are of the type that allow the head to be changed so a PITA but not the end of the world.

[Theo]

Most oil boilers are a simple 'burn when powered' arrangement. That power source will be looped through the heating/hot water valves: the controls/thermostat tell one of the valves to open, and when one of them has moved to the open position the switch on the valve will close and apply power to the pump and the boiler.

Sounds like the switch on the valve has got stuck. As you say you can change the head, or you could see if the switch is accessible and might be cleaned/lubricated to make it unstick. It may be a regular microswitch that could be changed without replacing the head.

Theo

[ARW]

Cheaper to just swap the motor. And often easier.

[Graeme]

In message <bwE* [e-mail]>, Theo <theom+ [e-mail]> writes

Excellent, thanks. I have given the head a 'gentle tap' and that seems to have released the micro switch, and all is well. I'll have a better look tomorrow.

[Harry Bloomfield Esq]

Graeme laid this down on his screen :

If it is the type of head which stalls the motor, rather than switching it off, powered against a return spring, they are under a lot of stress. They tend to wear, and jam. Better to consider replacing the worn head.

[Roger Mills]

I wish that all CH questions were this easy to answer. It's clearly an S+ system with a zone valve for each heating zone and hot water zone. Each valve has a micro-switch which closes when the valve is open. These switches are all wired in parallel, and switch on the boiler demand. It only needs one valve to stick open or one switch to fail in the closed position for the boiler to run all the time even when there's no demand.

I've got 3 zone valves in my system and have wired them all via 5-pin in-line connectors, which makes it very easy to replace an actuator without needing to get inside the rat's nest otherwise known as a wiring centre.