Main 24HE, need some advise guys...

[Blackadder43]

Hi all, long time no speak....
I have kept my Gas safety licence up but for the last 2 years have been concentrating on Power flushing, so am a bit out of the loop on boiler repairs.

My stepson phoned me up the other day and said his hot water was going hot and cold......
So today i picked up a DHW diaphragm kit thinking that was the problem...
When i got there and took the old diaphragm out it was intact, albeit a bit gunked up, so i changed it...

Fired the hot water up and the boiler tryed to fire a couple times then failed.
Reset it and tryed the hotwater again and it came on......but after a few seconds the boiler shut down, then a few seconds later fired up again..
Checked the min gas pressure and it was 10.2, spot on......
Fired the hot water again and the same thing...it fired ran for a while then shut off, then fired again.....
It looks to me like everytime the flame should be modulating it shuts down and then fires again....
During the few hours i was there it did flame failure a couple of times...
Because my head is a bit rusty on repairs i am not sure if its the gas valve not modulating or something else...
Any advise would be very gratefully recieved...
Many thanks...
Its a Main 24 HE

 

[Happyplumber]

Check the hot water NTC and change if necessary and more importantly clean out the secondary plate heat exchanger ,the boiler cant dissipatate the heat quick enough because the plate is blocked so it fires on and off thinking it has reached temperature and eventually locking out thus requiring a reset

 

[Blackadder43]

Thanks happyplumber
That sounds about right, stepson had a new bathroom fitted about a month ago that coincides with his problem starting.......probaly shook the pipes around and some crud has gotten in there....or just coincidence...
Plus the fact of hard water.......
Thanks anyway....appreciated....

 

[Baxmax]

What makes you think the Min B.P is 10.2

 

[Blackadder43]

What makes you think the Min B.P is 10.2

Its funny you mention that Baxmax
I rang my brother in law up earlier for some advise and he nearly fell off his chair when i said what i had set it at....
As i stated i have been out of the boiler servicing loop for a while although i kept my gas safe licence active...
Stupidly i was going by the manufacturers instructions in the manual, and they say that the minimum burner pressure should be 10.2........
I now know this to be incorrect and it should be between 2 and 2.5.....and will be sorting it in the morning along with the plate to plate........
I should realy edit this incase any "diyer" sees it and takes it as gospel....
Thanks
The boiler is also switched off and not in use.

 

[Agile]

This should have been posted in the CC area of the forum.

Tony

 

[Blackadder43]

Sorry Agile....i have just read up about "cc" section.....i honestly didnt know....will sign up later today if a mod would like to move this thread....
Sorry guys, i tapped the keys before reading the rules.....


Just tryed to register for the cc forum, i have put my gassafe numbers in although it was asking for corgi, i wasnt corgi registered, thats a time when i worked for my brother in law under his licence...
Hopefully all gets accepted and this thread can be moved.....