Boiler will not switch off!

[pamzer]

HI
need some advice. I have a Potterton Promax he boiler. Even with the CH and HW set to off on the programmer, the boiler keeps firing up every few minutes. I have replaced the programmer once, but it has started to have this problems again. I think its the HW that is calling for the boiler to fire up - Any clues please!

 

[ollski]

probably the microswitch in the hw actauator valve is stuck on, this will power it up without any demand for heat.

 

[pamzer]

Thanks for quick reply. Scuse my ignorance but is the micro switch located in the boiler itself or located near the hw tank and plumbing?? Is it big job to sort out?????

 

[ollski]

Im guessing in the airing cupboard you have two valves on the pipework with big square heads on the top and a wire going into each...have a look and tell us what you have.
Is the boiler indoors or outdoors?

 

[pamzer]

Im guessing in the airing cupboard you have two valves on the pipework with big square heads on the top and a wire going into each...have a look and tell us what you have.
Is the boiler indoors or outdoors?

Boiler is indoors. Found them in the airing cupboard. There are three grey boxes attached to pipe work. Think two are for ch as I have two separate thermostat controls in the house (one upstairs, one down). I assume the actuator valve for the hot water is the one closest to the tank. Have been stuck in airing cupboard watching to see if any movement as the system fires up - the little black switch on top appears to move on the central heating boxes, but not on the hw one. Does this mean anything??? I have manually fiddled (technical term!) with the black switch on the box and the hw appears to have stopped firing the boiler - not sure if its going to switch back on and off of its own accord. Will try again tomorrow. have noticed loads of limescale near where box is on the piping - could this be anything to do with it?? system is only 3 years old. Grey boxes are by Drayton. Thanks