Main 24HE - CH hot when DHW is called

[MrHockin]

Hi all,

After many faithful years, my boiler has started playing up! When DHW is called, both micro switches on the diverter are engaged (pins push out) despite the CH being off. A new diverter has been fitted, along with new PCB and AAV (old one was leaking). Boiler is a Main 24HE combi.

Does anyone have any ideas add to what it could be? Cheers in advance for any thoughts!

 

[CBW]

When the new diverter was fitted, were the sensing tubes checked and cleaned? What was the whole diverter replaced, and why was the pcb replaced?

 

[MrHockin]

Hi @CBW ,

Thanks for the reply. Sensing tubes checked no, diverter replaced upon recommendation, PCB replaced due to continual flashing power light. PCB cured the power light issue, problem with CH coming on remains!

 

[picasso]

possible blocked plate heat exchanger.

 

[MrHockin]

Thanks Picasso, something for me to check out. Interestingly, I emailed the diverter valve supplier originally assuming it was faulty, and they've told me it's likely a pump fault. It appears to be working fine to me, do you think there's a chance it could cause this?

 

[CBW]

A faulty pump will not bring the heating on. A blocked plate heat exchanger can send water down the flow pipe

 

[MrHockin]

I thought as much, thanks for confirming. I'll check out the heat exchanger and will let you know. Thanks for the help!

 

[MrHockin]

@CBW & @picasso

A new plate heat exchanger was delivered today, I've just fitted it, and everything's sorted. Thanks very much for your advice, it's truly appreciated!