Vokera 80sp burner problem

[JimmyMac]

Hi guys, my elderly Excell 80sp recently had a new main heat exchanger fitted as the original had corroded and leaked all over the main burner and everything else below.All seemed well after the repair then yesterday the pilot was out and the pressure down a bit.Upped the pressure to normal range and lit the pilot no problem but the main burner is refusing to come on either in dhw or ch mode. Going through the fault finder checklist I have the pump running,the fan running,water pressure and gas pressure,the gas valve is energising but still zippo ignition.It goes through the motions and sounds like it's ready to come on with the usual clicks etc but still nothing.
Any tips as to what to look at next?
Thanks in advance Jimmy Mac.

 

[newbie1]

have you checked air pressure switch and voltage at gas valve

 

[JimmyMac]

have you checked air pressure switch and voltage at gas valve

Hi newbie1,that was quick!
I'm getting 230v ac at the valve when calling for heat and zero when not.This seems to be in line with the MI.
The air pressure switch crossed my mind so I'll check that - a wee bit of work though to get at it.
Cheers for now.

 

[newbie1]

230v at gas valve is correct
it indicates a fault that is both common to heating and hot water so
pump/fan/aps need to be checked as operating
check ohms reading of pump/and fan with power off and voltage when on
check aps continuity common to nc and nc to no
if each component checks out then look at circuit board if it has one as next area

 

[JimmyMac]

I just nicked out to the plumbs merchant and got a new aps as the old one was very brittle about the spade clips although it seems to check out ok otherwise.While I was there a guy told me to check the venturi.
I'll do that first then check out your suggestions.

Well I've cleaned the venturi pipes and fitted the new APS but still no joy.Those readings you wanted are Fan 55.3 ohms stopped
158v slow and 242v fast.
Pump resistance readings were all over the place giving a different value each time the probe touched then going back to 1. I think maybe the big capacitor has something to do with that.The running voltage was 244.
What I have noticed is 10 - 15 seconds after shutting off the gas tap the gas valve gives a clonk and the control knob jumps out about 3/16ths of an inch.I don't know if that has any relevance to the problem .
I think I'll need to go back and get the pcb, it's the only thing left to try.I might get a high limit stat as well but I think that's clutching at straws as the pilot's working.

 

[newbie1]

power off measure resistance in ohms on the pump poss pump is either getting wrong signal from pcb or is shorting back to pcv..the gas valve is just locking out as it should its a safety device and if boilwer locks out gas valve must shut within 60 seconds
it is sounding like a pcb fault
most boiler repairs are trial end error as one fault can mask another hence customers get the hump
recent ferroli giving warning of low pressure in system and going to shutdown after ignition even with 2 bar pressure so you think faulty water pressure valve change it and find pcb is faulty so customer thinks youre useless and a cowboy trying to rip them off

 

[JimmyMac]

I've just put a new pcb in along with a new high limit stat for good measure and I'm still getting nothing. The pump feels as if it's running and I did the resistance test with the power off
I've found I can light the pilot with a very slight pressure on the GC knob but no matter how long I hold it goes out as soon as I release it,however holding all the way in keeps the pilot lit after release.
I can't help thinking there is something silly I'm missing here. Are there any other devices that could prevent the gas valve from opening?

 

[stevetheplumber]

I've just put a new pcb in along with a new high limit stat for good measure and I'm still getting nothing. The pump feels as if it's running and I did the resistance test with the power off
I've found I can light the pilot with a very slight pressure on the GC knob but no matter how long I hold it goes out as soon as I release it,however holding all the way in keeps the pilot lit after release.
I can't help thinking there is something silly I'm missing here. Are there any other devices that could prevent the gas valve from opening?

dont know the model but sounds like the thermocouple to me boiler wont light if thethermocuple isnt holding the pilot on its possibly a overhet interuptred thermo couple so check that for continuity first to test you can short the overheat out temporarily

 

[JimmyMac]

Hi steve ,the thermocouples on these very seldom fail apparently- if anything its the high limit stat that causes problems.In this case the pilot will light and stay on no probs - I was just faffing about trying different things to get the main burner on.When I noticed the gas control knob kicking out after shutdown I thought if I could get the pilot to light without pushing the GC knob all the way in then the burner might fire up.
I'm starting to think water has got into the gas valve but on the other hand it was going like a good 'un all night after the HE was changed so you would think everything was dried out.

 

[stevetheplumber]

in that case its the gasvalve thats faulty as everything else has to be inplace prior to the gasvalve opening which is all happening as you have 240 to the valve

 

[Puddle]

common fault on these boilers is that the gas valve push in knob sticks in when you release it after lighting pilot light therefore boiler burner will not light until arm pulled out although you will hear gas valve click when powered up
remove gray cover push in to light then pull metal arm out (do not twist)and if pilot stays alight boiler will light
lubricate matal arm to allow correct operation

 

[JimmyMac]

Re: Vokera 80sp burner problem - SOLVED!!

Hi guys - this is just to let you know the problem has been solved
Looking at the water in the valve idea I decided to go for broke before taking a sledgehammer to the old Vokera!
I separated the valve operator from the main body and and hosed them both with a hair dryer for about 10 minutes.After reassembly the old girl fired up after a couple of extra clacks and clonks!
So I'm a warm happy bunny
Thanks every body and a Happy New Year to you all.