Intermittent heating fault Gold Combi 24he A

[abc_plumb]

Hi guys
Need some advise on a mind boggling repair.

I've had a customer call me regarding his Potterton Gold Combi 24 He A (G.C 47-393-18)
He says when he comes to the office in the morning and switches the heating on, it doesn't fire up straight away. He has to turn the hot water on, then off again for the heating to work.
When the heating does fire up it works fine. He turns the boiler off when he leaves the office and turns it back on when he comes back in the morning.
Now this fault doesn't happen every morning, but on most occasions it does.

There is no room stat just TRV's which are set to max. (like always)

Anyone come across this before?

 

[abc_plumb]

Anyone?

 

[SmokeyJ]

As the heating is coming on once the hot tap is run would think external controls are working. No heating flow switch on boiler so nothing like that would hold it off. 3 way valve doesn't fire boiler just simply 'diverts' flow of water either to heating or hw. If valve stuck in hw position the boiler should still fire with a heating demand and just circulate through plate heat exchanger. More than likely a pcb issue, sticking relay or something and the hw flow switch kicks it back in? I don't think pcb reacts to 3 way valve in the way that boiler will only fire up if its motored over in the demanded position? Not too familiar with boiler just looked the mi's up, might help.

 

[abc_plumb]

Thanks Smokey
I hate these intermittent faults, hard to diagnosis.
Will take a punt at replacing the pcb.
Will let all the helpful engineers know how it went.
Or I man just tell you. Lol

 

[lame plumber]

i would check the diverter valve first, see if its stiff and not hitting the micro switches that fires up the boiler!

 

[tamz]

^^ i agree^^. Strip it down and clean it. Usually full of rubbish. 20 min job before you wase money on a pcb.

 

[SmokeyJ]

Does the diverter valve have micro switches? As I say never had to test one before, wiring diagram only shows 3 wires to diverter. Black red and white?
I wouldn't go straight in with a new pcb, defo needs a site visit and fault finding

 

[abc_plumb]

The problem with the site visit is that everything is working.
It's only that once in the morning, then it's fine during the day.

 

[abc_plumb]

Here is a clip of whats happening.

https://youtu.be/HDwGofgwllw