potterton Combi 80 no CH

[willhamlyn]

Hi I have a combi 80 which won't work on the central heating side.

It initially blew the fuse on the main pcb which I replaced, and also the user panel was replaced which brought back the hot water side

Now I just get the CH on for 30 seconds from cold and then the gas goes out, no lockout. if the boiler is warm the CH side will lockout and burner won't light, although I hear clicking as though it's trying to ignite.

I've removed and checked the diverter valve which is working fine (heat it it shuts, cool it it opens) Fan works, pump works, CH stat is ok (changed it anyway as had a spare).

Fault finder points to Boiler overheat stat so I briefly bypassed it and it keeps going, for a min at least but didn't want to let it run any longer than that, the pressure rose up to about 3 bar in the CH side.

I guess there is an overheating issue somewhere on the CH side but I think it's time for an expert now.

Anybody recommend somebody in the Deptford/Greenwich area who won't charge me an arm and a leg and knows what they are doing.

Thanks in advance

Will.

 

[Baxmax]

Check a.p.s tubes/venturi /switch

 

[willhamlyn]

Cheers Baxmax, why woould the hot water side of things work OK are there separate circuits?

is that something I can test myself?, I'm guessing they're on the gas side of things so expert time?

 

[Jezclayton]

I think you will find it is the wax cartridge in the diverter valve, deterioration of which means the diverter does not fully open. Sounds like everything else is working to spec.

I don't think you can buy these on their own anymore, so will need to buy the whole diverter. New diverter in hand it is quite simple to just swap the cartridges.

 

[willhamlyn]

That was my thinking, so I took it out and tested it, opens (closes depending on how you look at it) fully in hot water and closes up when in cold, it was only changed about a year ago as well.

Must be something else, BG coming Monday so I'll post the solution when I know.

 

[Jezclayton]

BG

 

[ChrisR]

They'll probrbly tell you you need a new boiler.

SParking but not lighting?
Are you sure?

 

[baxpoti]

Pumps, odds on favourite for me.

 

[Steve69the69Gas]

BG = 'you need it powerflushed for £600'

 

[Jezclayton]

Pumps, odds on favourite for me.

The OP says the pump works.

 

[Jezclayton]

BG = 'you need it powerflushed for £600'

Have they got a sale on at the moment? £600 seems remarkably cheap for BG.

 

[willhamlyn]

ok I knew I would get hassle for mentioning BG! but nobody else would come out this week, I have a young family that needs the heating and BG are £156 all inclusive of parts which I didn't think was too bad.

And yes the pump works, at least it whirrs and I took it out to test it and it spins under power, impeller seems firm enough on the shaft, I suppose it might be running too weakly when under load causing the overheat but we shall see!

Thanks for all the input though!

 

[steve32]

Diverter valve fully opens at approx 80deg within approx 60secs.
if as you say the pump is working ok then the boiler when on, heating will fire, hot water will circulate around the boiler, when the diverter reaches the above temp it will open allowing heat to heating circuit if the valve fails to open it will go to lock out or shut down.

 

[Jezclayton]

Just had a thought on this. You haven't got a dripping tap have you. I seem to remember even the slightest amount of cold water at the diverter cartridge will stop it opening properly. We use to test this temporarily shutting off the mains water at the boiler inlet.

 

[willhamlyn]

Hi chaps, well you were technically both right, an intermittently sticky diverter and a pump that was only failing when under load, both replaced and now all working again (until the next time!)

Thanks a lot for all you help

Cheers

Will.