Boiler operating CH even though it’s switched off !!!!

[wiffers2003]

My Potterton Performa 24 Combi boiler is switching the central heating on even though it is switched to hot water only on the front. Also, the room stat is on frost, and the timer on the boiler is off. How can this be ????

My rads are getting hot so I’ve turned them all off until I can fix it, but that obviously wont be any good for the winter as the room stat doesn’t seem to switch off the boiler (which is on hot water only anyway)……..huh !

I’ve disconnected the mains supply for half an hour to see if it might reset the electronics, but it made no difference.

Please help !

 

[Paul Barker]

If it happens when you run a hot tap diverter valve needs attention

if it happens regardless of hot water demand thermister needs attention

 

[ChrisR]

Boiler comes on if thermistor tells it it's very cold

 

[wiffers2003]

Could it still be the thermister causing the fault even though the boiler is switched to HW only?

Someone mentioned a lever to wiggle on the diverter valve, is this a common thing?

thanks

 

[Agile]

In my experience its almost certainly because the DHW flow microswitch has failed.

This is so common that I carry the part with me.

Changing it involves replacing a considerable part of the wiring harness and making the connections to the boiler's PCB.

If you must do it yourself then I hope you are able to deal with PCB connections. PCBs are very delicate!

Its not the recommended way to do it, but I have seem some people just cut the wires to the switch and join the new switch with a choc block.

Tony

 

[wiffers2003]

Hi Tony,

You seem confident that its the microswitch, have you seen this problem with this actual type of boiler.
Where can i find the microswitch, and where can i buy a new one.
I am ok working with pcb's as i work in the world of electronics.

thanks Carl

 

[Agile]

In my experience its almost certainly because the DHW flow microswitch has failed.

This is so common that I carry the part with me.

Tony

You are expected to interpret that as meaning that I work as a boiler engineer and that I have seen your fault so often that I carry the spare part with me anywhere I go. Its the most common fault I see on your model.

How could I have made it clearer ( without writing many more words? ).

The sensor will turn the boiler on if it thinks that its very cold to protect against frost.

However the sensors rarely just go high resistance and in frost protection mode they just turn the burner on until the output is at about 20°C.

Tony

 

[wiffers2003]

Yes indeed Tony, sorry i didn't mean to appear dumb. Just wanted to confirm if you'd seen it with my particular make/model which it seems that you have.

Thanks for the advice.

 

[namsag]

Bottom left hand corner round brass divertor with a pin that comes out when HW is demanded make sure this pin is returning when no HW is demanded if it staying out thats your prob

 

[wiffers2003]

Checked the microswitch last night, and yes Agile is right (i think he new that!). It sticks on (measures continuity) across the normally open terminals until you tap the switch body which then releases the contacts.
Just got to find a new switch now, any idea's of a supplier?

I see the pin on the diverter valve that should pop out which has slight corrosion around it. Would it be ok to spray a tiny bit of WD40 on to it to clean it up and lubricate?

thanks

 

[wiffers2003]

...........Also, would one of you fine people be able to confirm the part number of the microswitch as i am unable to track it down by searching on the web, and it doesn't mention it in the manual !

Many thanks !

 

[wiffers2003]

Its ok, found the part number (248207) and got one off the internet delivered for £18....bargain !

 

[Agile]

Its not a bargain if you need about 15 of them every year!

We pay a bit less but charge the customer £23 which is still less than the retail list price.

Tony

 

[wiffers2003]

That's very decent of you Tony. i can imagine that other people might take advantage and charge a lot more than that.

How long do you think the new microswitch might last, maybe i should get some stock?!?!?

 

[mattylad]

Jeez! thats a damn expensive microswitch.

Anyone got any pictures of it?

Having worked with them for many years microswitches can usually be obtained for a couple of quid so I'm curious what makes this one so special?