HELP! No Switched Supply To Boiler

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HELP! No Switched Supply To Boiler

Post  galewis on Fri Feb 10, 2012 8:44 am

Prepare for a tale of woe.

I noticed a sudden drop in the radiator temperature and hot water the other night. I checked the boiler (Glow Worm Ultimate 50FF) and sure enough, no pilot light. Swiched the boiler off at the isolator and back on and heard the relays click on, fan spinning up and 'hunt' and then relays click off again and repeat the cycle. After reading through the manual and noting the status of a number of LED's on the main PCB, I followed the fault finding flow chart and decided the fault was either with the air-pressure sensor or the main PCB. Whilst using a multimeter to test for voltage I must have shorted something because I tripped the whole house and blew a fuse on the main PCB. So, after replacing the 1A fuse I decided to replace the sensor first as that was cheapest, but it didn't resolve the issue. So then I changed the PCB. The replacement PCB was an up-issue from the original but all the connections seemed the same, and I was really happy when everything seemed to work when I switched it back on and the boiler fired up and all of the status LED's were as they should be.

Everything was fine for about 2 hours or so - hot water, rads up to temp again and then a horrible shuddering sound from the airing cupboard area - I immediately checked the boiler and noticed the pilot light had gone out and the overheat sensor had tripped. It was late in the evening now and I thought, 'maybe it's a one off whilst everything's getting back to normal', so I reset the overheat sensor. Everything fired up as it should and all was ok for about another hour. Then, same shuddering from upstairs. I go back to the boiler and, sure enogh, pilot light is out. This time however it won't restart. I'm thinking the overheat sensor is probably fried at this point and decide to call it a day.

Next morning I resign myself to get a professional in. I phone Glow-Worm and they send an engineer to have a look - He ultimately decides there's nothing wrong with the boiler and proves it by shorting two wires together at which point everything fires up as normal. I was dubious until this point as I'd convinced myself that it was bad wiring as a result of my DIY antics. The engineer goes upstairs to have a look at the BM2000 which he tells me he know very little about, but after a minute or two of checking voltages with his meter tells me that it's the BM2000 at fault. He tells me that 'there is no switched supply to the boiler' and that's why the boiler isn't firing up, and says there's nothing he can do. He then leaves.

Looking at the BM2000, all seems normal to me. The display with "-ON" on it is as it always is. I can hear water rushing around the radiators, the pumps at the bottom of the unit all seem to be doing what they should. LED 1 (boiler on) and LED 2 (Boiler Pump On) are both on. LED 3 (Heating Pump On) is off.

Can it be that I've had two independant failures on the boiler and the BM2000 within hours of each other? Seems improbable. Perhaps me shorting the boiler PCB has damaged the BM2000 in some way? Any ideas what the fix might be? New ACB perhaps, but it looks ok and the best quote I've had is £240 plus delivery for a replacement?

Thanks for taking the time to read this. I hope someone might be able to offer an opinion.

Gary

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Re: HELP! No Switched Supply To Boiler

Post  mike on Fri Feb 10, 2012 11:10 am

It looks like the Main ACB on the BM 2000 has gone.
If I fitted it I would remove the boiler wires before switching the unit on.
And test to see if the BM board is giving the switched supply.
If the boiler guy proved the boiler worked.
And that there is no switched supply ( check at the ACB)
Then it looks like the ACB.
Mike
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Re: HELP! No Switched Supply To Boiler

Post  galewis on Fri Feb 10, 2012 12:09 pm

Thanks Mike...

You're right, I've just disconnected the ACB and notice one of the 3 Sharp S26MD02's had fried (I guess shorting the PCB on the boiler PCB was the cause, which is a surprise as I would have thought the ACB would have some sort of on-board protection against this sort of thing. It is 'fused' after all. Smacks of crap PCB design on the ACB. Still.... my own stupid fault for not getting a pro to sort it out in the first place. Lesson learnt!!!!)

Anyway... the fried part is a solid state relay. I'm an electronics engineer by trade and from my brief investigations so far it looks as if this part is obsolete. However, Sharp's PR36MF21NSZF (Farnell part no. 1618484) looks like an ideal drop in replacement, so I've ordered one because it's worth a go for £1.50. Most likely other stuff on the board has fried too (although no visual evidence that this is the case) but he who dares....

Otherwise, I guess it's £250 for a new ACB, unless anyone knows anyone doing refurb boards?

I'll report back if it works. If it does, I might be able to return a favour to the board members in the same predicament.

Cheers

Gary



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Re: HELP! No Switched Supply To Boiler

Post  mike on Fri Feb 10, 2012 12:30 pm

If you look through the posts, there is a guy who will try mending them.
Mike
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Re: HELP! No Switched Supply To Boiler

Post  galewis on Sat Feb 11, 2012 8:01 am

Just thinking about this a bit more Mike...

I've no doubt that the ACB needs replacing, but my concern is that the boiler might still have a fault.

What do you think of this reasoning:- After replacing the boiler PCB, the horrendous noise I was hearing from the airing cupboard was, I presume, boiling water in the expansion tank. If their was a fault on the BM2000 and it was calling for more hot water from the boiler, I'm thinking there's nothing that the BM2000 can do to cause the overheat sensor to trip in the boiler, is there? For the overheat sensor to trip, surely the fault can only be with the boiler. If I'm right, I could replace the ACB on the BM2000 and, because of an existing fault on the boiler, it will destroy the ACB again.

I'd really appreciate your opinion.

Gary

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Re: HELP! No Switched Supply To Boiler

Post  mike on Sat Feb 11, 2012 11:10 am

That is what my reply to you was.
Ref a possible fault on the boiler.
So you could connect the boiler live and switched live, N & E via a lead / plug etc.
Try it that way.
But not for long as the boiler pump in the BM will not be running.
You could also connect the boiler pump in the BM to another supply just in case that is faulty.
Checked the ACB for fault codes?
Mike
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Re: HELP! No Switched Supply To Boiler

Post  galewis on Wed Feb 29, 2012 12:09 pm

Hi Mike

Hoping I can trouble you for some more advice. I'm still having a problem with no central heating. The boiler now works fine and heats the store up effectively and will cut out when the maximum store temp is reached at 77C and come back on again at 74C as seen in the ACB diagnostic. However, no hot water for the rads. I know the pump is good because the system works fine in immersion heater 'switch' mode. LED 3 on the ACB doesn't come on, so I thought ACB fault. I've now replaced the ACB with a new one, but the problem remains. I've run the diagnostic on the ACB (jumper 5) and all seems ok, so I'm running out of ideas as to where the fault is. I'm thinking perhaps it's the thermostat? Is there any way to temporarily short two terminals together on the boilermate to simulate 'thermostat on' to check?

Thanks in anticipation

Gary

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Re: HELP! No Switched Supply To Boiler

Post  mike on Wed Feb 29, 2012 3:14 pm

Have you tested the pump for a supply when the heating is on?
Have you checked the room stat?
You should have a switched live at the stat.
Check the pump connection etc at the ACB
In fact all the connections
Mike
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