My Vokera Excell 80E automatically on and always stays on

[winstonscotland]

I hope someone here can give me a clue.

My Vokera Excell 80E has been working for many years, it was under Scottish Gas Home care program for some years until recently they said spare parts are running low and they cannot guarantee any fix if problem happens.

The problem did happen now. The boil appears fire up even turn off the timer. it seems the timer control is bypassed. The central heating is constantly on. I tried to identify the problem and checking the ignition block (PCB 7097 or BC03), for some reason, when I unplug the connectors and replug all the connectors back, the problem become worse. the boiler did not fire up anymore. sounds like a deaf became a blind after my treatment, not great. I checked the PCB based on diagostic procedure and found there is no power feed to fan anymore.

Today, I bought a reconditioned PCB, when I installed it, the boiler immediately fire up again like before and bypassed the timer control again. It seems the problem is still there. I run out of ideas now, I really appreciate if anyone can shed some light here on what could be a possible reason. thanks!

Winston

 

[dcawkwell]

Could it simply be the timer is faulty?

Or would that be too obvious?

Rather than looking for complicated pcb solutions.

 

[winstonscotland]

Thanks for the promptly response.

I did check the timer function first and the timer link appears functioning properly. I also disconnected the timer to ensure the link is broken (although it has been confirmed by meter), still the boiler will automatically fire up. Thanks again for your suggestion!

 

[Agile]

I am not in favour of repaired PCBs.

Furthermore, if a boiler is faulty then unless the cause of the fault is obvious its usually more convenient to get a competent boiler engineer rather than replace parts which are not at fault.

Diagnosis is a matter of testing.

Tony

 

[winstonscotland]

I appreciated your quick response.

On one hand, I can agree to certain degree about your attitude towards reconditioned PCB. The reason I choose the reconditioned PCB is:
1, The new one cost over 200 pounds, and reconditioned cost 70 pounds
2, I tend to believe those repair engineer understand what they are doing and normally I do not think the PCB can go seriously wrong. For this particular case, I reserve the opinion now because I need to find it out yet.

 

[dcawkwell]

Frost protection kicking in if the boiler has it. (haven't checked)

Faulty sensor.

 

[Agile]

I suspect its something very simple indeed.

But I dont make guesses.

Tony

 

[winstonscotland]

dcawkwell, I think the frost thermostat sensor issue is a really possible logical reason because it can override the other switches, I just checked the boiler again now before I type this response, it appears it is not installed. thanks for the constructive suggestions!!!

 

[Agile]

Winston, DC was refering to the internal frost protection facility which many boilers have and not to an external one as you thought.

Have you tested the operation of the DHW demand switch which is activated by the fulcrum arm?

Alternatively, which control knob seems to alter the flame height when turned on the front panel?

Tony

 

[biscuit77]

Winston i agree with agile..the most common reason that model off boiler does that fault is the domestic hotbwater microswitch sticking. You can't repair it you'll need to replace it easy job though the switch comes with new connectors etc it costs about 15 quid.[/img]

 

[winstonscotland]

Thanks Agile and biscuit77 for the constructive suggestions. I think the suggestions are pointing something closer.
1. I do not know about the internal frost protection, I did only check if there is external one installed, which should lie just beside the timer switch if installed. For this lead, I have not exhausted the possible cause yet, I need to find where is internal one if installed. But the other suggestions might more important now.
2. When the central heating is on, it is the DHW temp control switch appears control the flame, when it is turning to low temp, sometimes, the fire can be stopped for a while then back on automatically again. Sounds like it is something related to hot water demand part. When a change the CH swtich, it seems not very responsive. Seems something is there.

Thanks for everyone participated!!! All the suggestions are really encouraging!

 

[biscuit77]

Definately the sounds like the dhw microswitch the mate.

 

[winstonscotland]

ho...la...

Thanks everyone so much, finally I got it, I took out the micro switch and enforce to be isolated, bang on! biscuit77, it is the sticky micro switch. Guys, if you are around Glasow sometime, I'd like to buy you some pints. I am an academic and enjoy DIY and sometimes probably too bold, but the rewarding of my involvemnt in getting the job done is so enormous that I simply cannot resist. I am happy to give the guy 70 pounds even though my original pCB may not be faulty. But without you guy's help probably I won't be able to carry on. So many many thanks!!!

 

[DP]

Winston, firstly I have to say your boiler needs a proper service. Breakdown cover you mention does NOT automatically mean boiler gets service as described in the manual.

Stop wasting time and money and get the boiler looked at with a view to servce and repair. I do this day in day out and carry many parts for this boiler for single visit repair and service. Your attempt is a hit and miss method that is hitting your pocket but missing to effect a cure. No boiler is going to keep working if manufacturer's recomended service is not carried out. Flue gas anayser will point to poor combustion but it certainly does not show malfunction in water carry components. A blind man with a stick could identify poor combustion on this type of boiler let alone use a FGA that is common practice with many large organisations who provide a 'boiler breakdown service' which is NOT a service BUT a SAFETY check.

Do not know where frost protection is coming into the picture. Do conceed the point that couple of morning has been a bit frosty but do not see any black ice or negetive temperature figures that would cause the boiler to kick in- anyhow, if that were the case, once rooms come up to temperature, frost protection would be satisfied and boiler would shut down.

 

[Agile]

When I posted at 1030 on Tuesday I had that switch in mind.

However, as you seemed to think buying a repaired pcb was a solution rather than calling an engineer, I was not in a hurry to suggest what the problem was likely to be.

Tony