WB Greenstar 2.5a fuse blowing

[larkim]

We've had a couple of instances of the 2.5a slow fuse blowing on our 2 year old WB Greenstar 30CDi boiler. Keen to avoid bank holiday call out charges (!), and knowing I can self replace this, I will do. However, I know that blowing a fuse means something else is wrong.

The fuse appears to be the fuse between the mains supply and potentially the transformer (though I'll admit I'm not too clever at reading circuit diagrams so that could be wrong) and I'm changing the fuse on the advice of the plumber who was called out to it last time - he advised that it was a "user serviceable" fix.

Has anyone seen anything similar in these boilers and could advise what the likely problem might be?

Thanks!

Matt

[geoff]

In message , larkim writes

Transformer open cct? Fan stuck? Diode bridge gone short cct?

[Donwill]

Damp electrics due to a short term freezing of the condensate pipe perhaps? It happened to a friend of mine, and cleared of it's own accord as boiler dried out. Don

[Tabby]

Maybe show us the circuit diagram. You have a multimeter?

NT

[Donwill]

Just to recap, I think you said it is an intermittent fault, how many times has the fuse blown and over what time period? My friend's boiler is installed in the loft and has been subject to extreme swings of temperature in the last few weeks and therefore highly likely to have had condensation problems. Don

[larkim]

To answer the various questions:-

- link to circuit diag (its the fuse next to ST10) -

the fuse first blew on 27th December, replaced on 28th (expensive fuse that one, needed a bank holiday call out!). Second blow was last night (2nd Jan) with normal use of the boiler between the two blows.

- temp changes? Not too much, its in a utility room, though there is quite a bit of condensation in there I guess as SWMBO uses the room to hang clothes for drying.

Cheers!

Matt

[geoff]

Ah - didn't read the "couple of instances" properly

-Fan sticking or wire chafing

[Sue]

may well be moisture in the pump motor, you would need a insulation resistance tester to check it

[larkim]

OK, more trouble. Replace the fuse with a 2.5a time delay fuse from Maplin today, and after about 6 hours of the boiler working fine it tripped tonight, this time the 3A fuse for the spur which supplies the boiler. Replaced that and 10 seconds later that same fuse blew again.

The transformer inside the boiler feels quite warm, don't know if that is a symptom or a cause. Anyway, a pleasant end to the Christmas break......

Thanks for all the helpful answers so far. Unfortunately most of the pointers appear to be towards things that I know nowt about, so it will be another call out I think!

Cheers!

Matt

[geoff]

Well, as someone else pointed out and I should have said - check your pump. Open the electrical cover and take a look inside for water / condensation

It's unlikely to be the pcb if you are intermittently blowing the fuse, that pcb doesn't tend to suffer from bad joints and they wouldn't cause such problems. You could check for water on the pcb surface, is there a leak which is dripping CH fluid onto the pcb ?

It has a DC fan - if it stalls, the stall current is higher than the "rotating" current.

Check for chaffing of wires in the loom on sharp edges of the frame. check for melted insulation

[larkim]

Got BG to come and take a look. Prior to him visiting I replaced the

3A fused spur fuse (this being about 12 hours after the failure) and lo and behold it all fired up. Giving credit to the BG guy, he still spent a good 1.5 hours looking over everything on the boiler to see if he could find the problem, as by then it was working fine!

Had been up from lunch on Tuesday then until this morning - its gone again!

All credit to BG, they will have someone out this morning, and we've run out of 3A fuses so I can't replace again!!

At least someone professional (I know opinions about BG will vary!) will be looking at it rather than me. Fan or pump remain prime candidates for looking like the point of failure, as has been very helpfully pointed out here.

I look forward to a shower when I get home!!!

Matt

[larkim]

They just left, replaced the fuses and boiler fired up again. Unsurprising but disappointing! However, as this was a repeat we're now booked in to have a new pump installed tomorrow to determine whether that was the problem or not. If it blows again, then they'll swap the fan. If it still blows, then something else etc etc.

Can't complain, all covered by the =A399 fixed price fee for calling them out! (Though I did have to take a service contract for 12 months with them too to get that fixed price call out, so its really actually cost me quite a bit more than that!)

Matt

[larkim]

You know, SWMBO may have solved it. She found this in a cupboard (the pump and actuator for the underfloor heating)

like there is definitely an opportunity for water and electricity to be mixing here.....

Matt

[Bob Eager]

You'd have thought BG would have checked that...

Actually, on second thoughts, *BG* wouldn't...

[larkim]

Yup, surprised they didn't spot it. We've isolated the UFH now so any new trips would have to be boiler related.

Could be an expensive part to find!

Matt