Grant outdoor combi

[lennytheloon]

Evenin all.


I'm after a bit of guidance really on a Grant outdoor combi 90 V3.


I believe I've diagnosed the fault correctly but the customer is refusing to accept it.

Does anyone have any real experience with these little fella's that I can bounce my findings off??


Cheers.

 

[ecowarm]

whats the problem
lenny

 

[lennytheloon]

Hey, thanks for the reply.


Ok so, I had the phone call to say the boiler wasn't working at all, no CH or DHW. I'll do my best to describe the symptoms without offering my diagnosis and see what you think.

Firstly the install is pants, pipes and cables just appear through a big hole in the wall of the house and drape themselves down into the boiler.
I have L&N supply to the boiler via a plugtop, a 3 core and CPC to an external single channel programmer and also a roomstat. Now when either the hot tap is opened or the roomstat calls for heat the pump within the boiler starts up BUT the burner does not. Also the burner does not operate but the pump does, via the test button on the front of the panel.

I've traced through and tested all control wiring over and over, from what I can see the pump operates independantly of the PCB whereas the burner recieves it's signal via the flowswitch at the back of the boiler and then through the PCB.

When I disconnect the return from the flowswitch and the SL to the burner from the PCB and bridge them out, and manually hold the flowswitch closed the burner operates and runs fine on CH and DHW.

Any questions please ask.

 

[dontknowitall]

Is there power in the zone valves? Coincidentally, I went to a boiler yesterday with what seems like identical wiring to this situation. Phoned my friendly helper and he told me to move the lever across and hey presto!! (On the one that worked that is!)

 

[lennytheloon]

It's a combi......no zonevalves.

 

[tamz]

Probably the burner flow switch

Check for 240 on burner live on pcb.

 

[ecowarm]

I would say overheat stat if you've bypassed pcb

 

[dontknowitall]

COUGH ... ooops!!!

Sorry!

Been a bad week so far ... not getting any better by the looks of things either ...

 

[Puddle]

I do not know boiler
however
you have linked out flow switch and still not working,you link flow switch direct to burner ok

therefore fault between flow switch and burner,quich heh,as said points to maybe high limit,has this been tested,boiler stat or dry joints on pcb,as said ,do not know boiler ,just some thoughts,anyone found a wiring diagram ?

 

[lennytheloon]

Thanks for the input.

No overheat or lockout lamps are lit at any time, nor is low pressure lamp.

I have 230V leaving the overheat stat on the black core of the 3 core flex to the pump & burner flow switches, these are N.O. Now this is where I lose my way a bit......I assume the flow pressure closes these microswitches as I can just see a small pin poking out of the pipework assembly, this however does not seem to be working as I have to manually close the switches to get my 230V supply back to the PCB via the brown core of the 3 core flex and consequently out on an orange core to the burner live terminal. BUT even with the microswitches closed, I still have to bridge out the 230V at the PCB to fire the burner, whilst the pump is running fine.

 

[tamz]

The power goes through the limit stat before the burner flow switch. If flow switch proves check for 240 on burner live on pcb. If not then pcb fault.

 

[Puddle]

Not that it matters as probably you would just replace pcb but does power come back through flow switch into pcb and into relay to send power to burner,as if 230v bet relay fused

Not that it matters as probably you would just replace pcb but does power come back through flow switch into pcb and into relay to send power to burner,as if 230v bet relay fused together

 

[ecowarm]

[DLMURL]http://www.grantuk.com/userfiles/download_25.pdf[/DLMURL] wiring diagram on this link

 

[lennytheloon]

Many thanks ecowarm.

My particular model's diagram is on P45. The issue appears to lie between 7 - 8 on the functional flow diagram.

My initial diagnosis was the PCB but the customer wouldn't accept that. The only thing that concerns me is how the flow switch actually operates i.e what actually causes it to close the N.O contacts on the pump and burner flow switches is it the flow, return hot, cold etc etc. This is the bit I dont undestand not being familiar with the whole pipework side of things so am unsure as to wether something here is faulty aswell as the PCB.

Can anyone clear that up for me.

Thanks.

 

[ray.call]

Hi lads
kenny im having the same problem myself. I got a new pcb and changed it and nothing same old story. The onle thing I can come up with is that I got a faulty pcb if I only knew how to check pcb it.