MegaSack DRAW - This year's winner is user - rgwb
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Having some issues with my heating. The plumber is off on holiday. Hoping the STW hive mind will help.
Have a Worcester Bosch oil boiler, pressurised water tank, drayton programmer and Honeywell room thermostat. Issue is that intermittently the CH won't come on using either the timer or by manually switching via the programmer. The boiler does not fire. As soon as I switch the HW on the boiler fires and hot water is pumped to the rads. We have always had independant controls for CH and HW and only recently has started mucking up.
Went into the garage where the boiler is and also went under the floor to check the 3 port valve which is in the auto position. I assume the water pump is ok as it works when HW and CH are on together. Does anyone know if a failing or stuck 3 port valve would stop the boiler firing if CH only is selected? I've checked the wiring end to end and can't see any loose connections.
You've diagnosed a common problem - the synchronous motor on top of the valve has failed. Take it off and go to a plumber's merchant, they will try to sell you the whole valve saying they won't take the motor back if the problem turns out to be the valve. But they very seldom fail, it's just a small rubber ball moving on the end of an arm on that spindle to block the ports. You can test the action with some pliers once you've removed the motor.
The motors are quite pricey.
One of these:-
http://www.screwfix.com/p/drayton-synchronous-motor/28670
£15.49
Most likely it is this ^^^ but there is an outside chance the microswitches on the valve may have failed or the lever that closes them may not be making full contact.
As above. Got the MiL's one working, for a couple of days, by shoogling the lever. Same symptoms as yours. BG took two months to diagnose the fault even though I told them what I'd done as a workaround 🙄
Go to a plumbers merchant and you'll get a synchromesh motor for about £8-9 +vat. Make sire it'll fit your valve, some manufacturers you can't replace the motor so have to buy the actuator head for the valve. Take the head with you if in doubt.
Thanks all. I'll strip it down tomorrow and take a look. Sounds like it might be a simple fix