Main 24 HE overheat

NW6 · 3 Mar 2011

Hello there

Just registered with this site. I am an RGI. Got a problem with a Main 24 HE combi continually shutting down on CH demand (but no problem on HW) and would be very grateful for any help; I'm going to site again tomorrow.

Burner is shutting down about 10 seconds after ignition on CH demand and then tries to re-ignite about 5-10 minutes later. Boiler is NOT locking out.

Thought at first it might be a flame recognition issue - re-adjusted the minimum gas pressure to 2.5mb as per manufacturer's spec; no joy. Replaced the flow sensor; again no joy. Looks like the boiler is shutting down correctly on overheating.

Having tried the basics, seems like it must be circulation problem i.e. a blockage in the systyem as the pump seems to be fine. The flow pipe above the diverter valve is boiling hot but not so below the diverter - big temp difference. Could there be a problem with diverter valve - perhaps its not returning fully to CH position causing the flow problem? Or it could it be a blocked bypass - if so could someone please explain to me how a blocked bypass would affect the function of the diverter valve?

All help greatly appreciated.

Thanks

NW6

paulthegas · 3 Mar 2011

flow and return isolations open?!

NW6 · 3 Mar 2011

Ya, thought of that one but no. Would have been a nice repair call-out but not to be.... Ta

misterdubya · 3 Mar 2011

Why did you think its a flame 'recognition' issue that when it works for Hot Water?

Best get your multimeter out once your back tomorrow. Nothing complicated on that appliance atall to be honest - but as an RGI myself I think you will fix it pretty quicky. It can only be 3 or 4 things, all easily tested.

Mr. W.

paulthegas · 3 Mar 2011

ha! worth a go! then probably diverter valve stuck in hot water. not familiar with a main boilers though.

NW6 · 3 Mar 2011

flame comes on max for HW; low for CH. Hence flame recognition probs sometimes on CH demand only

NW6 · 3 Mar 2011

Hey Dubya, will a blocked bypass affect the diverter valve...? I'm defo it's not a problem on the demand side.

paulthegas · 3 Mar 2011

does the return within the boiler get hot? it just sounds like the water is going around the hot water circuit all the time

misterdubya · 3 Mar 2011

NW6 said:
flame comes on max for HW; low for CH. Hence flame recognition probs sometimes on CH demand only

Eh? Explain please.

Mr. W.

NW6 · 3 Mar 2011

No, very little heat on the return. What heat there is could even be coming down from the hot water circuit

misterdubya · 3 Mar 2011

NW6 said:
Hey Dubya, will a blocked bypass affect the diverter valve...? I'm defo it's not a problem on the demand side.

No.

Stamina · 3 Mar 2011

join the cc

NW6 · 3 Mar 2011

Agile · 4 Mar 2011

Did you remember to clean out the return filter?

The CC is a closed part of the site where we can gas!

NW6 · 4 Mar 2011

Cheers, Agile. Ya, I'm going to do the return filter when I drain down today - I just think it's a problem around the DV because of the big temp diffference. By the way, where do I find the CC part of the site... can't see where it is

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Main 24 HE overheat

Stamina

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