Combi - replacing circuit board

[Geoff Pearson]

A very helpful engineer called today to look at the combi - boiler which makes good heating but feeble hot water. The conclusion is that the gas pressure after the modulating valve is too low: 4-5mB whereas the Glow-worm Compact 100e instructions say this should be 15.5mB from cold. The mains pressure is 21mB. It is not the thermistors, checked by swapping for new. So it is either gas valve or the PCB.

New the PCB is about £135 but a refurbished one is to be had from an eBay supplier at £50. I am minded to try the refurbished - I can do the swap easily. But I suppose I need to get the engineer back to check the pressures - a gas manometer is a specialised tool. Or I might chance that the potentiometers on mid-setting are about right - better than now anyway.

I don't mind getting the man back at £48 per hour - it would take only 10 minutes and if it is not the board then I need him to change the gas valve anyway. Anyone any advice on this?

[fred]

In article , Geoff Pearson writes

Do you have a multimeter that you could perform some tests with?

The thing to do is to operate the boiler alternately on heating and then on hot water, and check the gas valve control voltages. If they are within spec then it is reasonable to assume that the gas valve is not operating correctly but they are not then expect a problem with the board, or that the helpful engineer or someone else has been fiddling with controls that they didn't understand.

The installer manual is not particularly helpful in this area but it does tell you what to expect on the gas valve control wires under full demand, See the table at the bottom of page 29 To Check for Component Operation/Failure under Section 13.1 Fault Finding.

See also Section 10.5 Gas Rate Modulation and diagram 10.2, a competent technician really should have checked these things out.

Manual here:

you want a board then look know further than our own Geoff at but don't hang about it looks like they're shutting down from Christmas from noon tomorrow.

[Geoff Pearson]

I had downloaded the manual - after the engineer had been. I'm a licensed radio amateur (GM8BHR), have a degree in physics and used to be in electronics (but I'm colour-blind). The engineer, with my help, checked the voltages. They are 24-26v, unchanging - no matter what the pots are set to. Glow-worm, on the phone, said the voltage would vary 24-50v (as does page

29). Nothing moves a mV on my board. However, page 22 says set up with a pressure reading and that is my problem. The boiler fires up and runs, heats radiators and some tap water - but flame size looks a bit feeble.

[fred]

In article , Geoff Pearson writes

The manual isn't the most detailed in this area but let's assume that

24V is for minimum modulation and that 50V maxes it. If you've checked the inputs to the system and the outputs aren't performing as expected (not maxing on h/w demand) then it is pointing to the board.

You don't need to rely on the colours for the fault finding as the positions of the outputs on the board are shown on the diagrams, just count pins.

By all means get the technician back in to set your pressures accurately (if you're not confident using a manometer (or making one) yourself) but you should be able to see if they are substantially correct from the size of the flame.

[geoff]

In message , fred writes

Yup, out tomorrow SHOULD be delivered on thursday, don't hold your breath, the couriers are under pressure

It sounds like its not an urgent problem, i.e. the boiler is still actually working. Modulation control is a fairly common problem with compact 80/100 pcbs. I think I have some left in stock

buy from ebay at your peril. If its the company I think it is, they have just had a £250,000 CCJ against them from HMRC for tax evasion

[Geoff Pearson]

I ordered from CET this morning and they think it might be here on Christmas Eve. Great service. Geoff

[Ben Blaukopf]

On a related note - the rubber hose for my manometer has a 1/4" bore. It fits just fine over the test point in the boiler - but not the test point in the boiler, which has an external diameter rather larger than

1/4". On the basis that "if it's that difficult, you must be doing it wrong", there must be something I'm missing....

I've found this part -

which will clearly do the job, but I can't believe this is the only way of doing it.

[tony sayer]

Just second that!, he got us out of some serious bother last year in the coldest bit of the year;!...

[fred]

In article , geoff writes

Thought I'd heard you say something along those lines before but thought I'd let you issue the warning first hand. Certainly safer to deal with someone like yourself who has an established presence, has their own website and is available on the phone for queries.

[geoff]

In message , Geoff Pearson writes

We do our best

[geoff]

In message , fred writes

Received this today

I thought I'd share (a board we send out with a 12 month warranty for £50 ++)

"Hi, I found you via Google and wondered if you would be interested in purchasing a failed PCB from me? Part number 87483004170 (photo of actual PCB attached).

It is from my Worcester 24si ii which was intermittently not lighting, the boiler switched on but there was no ignition spark and it would eventually lock out. The board has now been replaced but I have a feeling the old one can probably be repaired.

I noticed someone selling the same faulty board on eBay for £40 + delivery

28Si-II-24Si-II-/261144861681). Would you be interested in this for £30 and I will include delivery in that"

made oi laff, anyway

[Geoff Pearson]

geoff

my board, ordered from you on Friday arrived this afternoon - so will have a session on Boxing Day fitting it and getting the old one back to you pdq.

Geoff

[geoff]

In message , Geoff Pearson writes

Wait till the new year to send it back, less chance of it getting lost