[SOLVED] GlowWorm boiler problem

[Roger Mills]

In my holiday flat I have a GlowWorm Ultimate 30FF boiler - installed new by the previous owner in about 1999.

As I was about to leave today, I noticed a loud buzzing noise coming from the box which houses its PCB - which I can best describe as sounding like a mains hum plus a load of chattering relays. Also, the pump was running, even though there was no HW or CH demand (it's an S-Plan system) - and hadn't been for far longer than could be explained by pump over-run. The noise stopped when I removed all power to the boiler. [There's a permanent live, even when there's no demand].

I assume that something is amiss with the pump over-run circuitry - which I assume is housed on the main (only?) PCB. The PCB was replaced about two and a half years ago in order to fix a firing fault - and I still have the old board.

Am I going to have to replace the PCB *again* - maybe getting the previous one re-furbished by Geoff - or is there some other explanation for my symptoms?

[geoff]

In message , Roger Mills writes

Chattering relays - can only be the pcb really

There are two versions of the ultimate pcb - one which controls the pump (2 fuses on the pcb, 7 flying leads) and the other which has one fuse and 5 flying leads

I presume you have the former, from your diagnosis

[Brian Gaff]

Power supply failure?

Brian

[Brian Gaff]

Yes sometimes if its a bridge rectifier a problem happens in a cap that makes it draw more than expected at start up if its been off and this tends to manifest itself as one leg going down. Fit a more butch bridge and renew caps.

I hate control electronics for most things.. grin.

Brian

[Roger Mills]

Yes, my boiler does control the pump. I do indeed have two fuses and 7 flying leads (plus plugs for gas valve, fan, pressure switch and electrode).

One thing puzzles me though. There seem to be two versions which both control the pump - 900847 (the one listed in the installation manual) and 202268 (listed on the CET site as being for the Ultimate 50). They both have two fuses (albeit in slightly different places) and 7 flying leads. Is there any significant functional difference?

The new board which was fitted a couple of years ago (not by me) appears from the packaging to be a 900847 whereas the one which was removed - which I'm looking at now - is a 202268! Any comments?

[geoff]

In message , Arfa Daily writes

This is one of those occasions to stick to the burger bar, Arfa

[geoff]

In message , Brian Gaff writes

Brian - If you can find a bridge rectifier in an Ultimate boiler, I'll restore you to 20/20 vision

[geoff]

They are the same

Just as the the predecessor (single fuse) started out as the 202042 and then became the 202233 (202142 being blanked out with a black indelible pen and 202233 being on a plastic label inside the perspex). These were then replaced by the functionally identical 202200

[John Rumm]

More milk tibbles...?

[geoff]

In message , Arfa Daily writes

These simple sequence boards just use C-R droppers,

you went off on a bender in a completely wrong direction

Have you seen me miss a chance to take the piss?

I rather think not

[Dave Plowman (News)]

Amazing on such an expensive device.

[geoff]

In message , "Dave Plowman (News)" writes

You have sussed my business model

The potterton profile pcb has 3 transistors and retails at over £200 I do it for £30

The thorn apollo fanfare fan (shaded pole motor and some bent bits of metal) is over £300 I do it for £45

[Russ17]

I had a problem on my Ultimate 7 wire 2 fuse PCB - when circulator (pump) reached the end of over run, the control relay (RL3) would chatter for 2 seconds. This gradually increased to 10 seconds and eventually, the relay chattered constantly. I traced the problem to C4 (100uF 50V) which is a smoothing capacitor for half wave bridge rectifier formed by D1 & D6. The Permanent live is dropped by a 220 ohm resistor (R31), then a 1M5 ohm resistor (R9) in parallel with a 330nF capacitor (C2) then half wave rectified by D1 & D6 and smoothed by C4. This results in about 42V DC as a supply to just the circulator relay (RL3 - Panasonic JS1-48V a 48V DC coil relay). The relay is configured such that the pump runs always when the relay is OFF but pump stops when the relay is energised (which is most of the time). Replacing C4 with 100uF

50 V electrolytic capacitor solved the issue. The faulty capacitor caused the supply to drop to 36V, which is just on the lower limit of the relay coil holding voltage so it was chattering as it could not be held energised under these low voltage conditions.

[Russ17]

replying to geoff, Russ17 wrote: Bridge Rectifier is formed by D1 & D8 - the DC is smoothed by C4 (50V 100uF) In my case, this caused a low DC voltage (approx. 36V) which was too low to hold RL3 (Circulating Pump ) in, so it cycles between on & off. The voltage should be around 42V DC to drive the relay coil which is 48V DC.

[Brian Gaff]

Well there was one in a friends boiler, but it was a long time ago now. It was one of them fourlegged epoxe square things with a hole through the middle and it seemed to have died because it was not rated for the surges, only themean current taken. Brian

[tabbypurr]

[KC]

replying to Russ17, KC wrote: Thanks for this, excellent diagnosis. Same problem cured.