Combi boiler has gone pop

[Rednadnerb]

I let the central heating pressure on my Gloworm Swiftflo combi drop to the point where the red flashing warning light came on. The boiler was switched off at the mains by someone who thought it was dangerous. Next day I turned the valve to fill the CH pressure up to just above one bar then switched the power back on. The boiler made grumbling noises (which it might have been making before - not sure about that) then there was a pop and the lights on the boiler went out. Now water is leaking from a pressure release valve inside the boiler.

My question is what what happened and what do I do to fix this?

Please don't say call a Corgi registered engineer, I'm not about to go sawing through any gas pipes.

Thanks for any advice.

Brendan.

[NOSPAMnet]

I guess it's out of warranty?

[Andrew Gabriel]

Primary heat exchanger could have had air in it if pressure dropped very low, or system had an airlock so there was no water flow and it boiled in the primary heat exchanger. I don't know that boiler, but there may be an overheat trip which needs manual reset to get the boiler back on. I suggest you don't do this until we better understand the other things which have gone wrong.

You didn't notice what happened to the pressure when this was happening?

It could be that the pressure relief valve, having operated for some as yet unexplained reason, now has debris jammed on its valve seat and won't shut off again. Manually operating it in this case might flush the debris away. What does the pressure read?

Is this continuing non-stop at a high rate with the filling loop disconnected? If so, it sounds like the plate exchanger has burst, bridging the water supply to the heating circuit. If it stops when you turn off the cold water feed to the boiler, that would confirm. This seems unlikely given that the other side of the plate exchanger should be higher pressure and the PRV should have protected it.

Insufficient diagnosis as yet.

[chrisj.doran]

As _all_ the lights have gone out and if it wasn't a big "pop", I'd begin by suspecting a fuse, either in the mains plug/connection or somewhere inside. A sensor trip normally leaves at least a fault light on. The blown fuse may indicate a real fault (if you have a meter, check for an L-N or L-E short) or may just be due to a switch-on surge. If you replace the fuse, switch on, and be prepared to switch off smartly if the grumbling gets alarming, but it might just be air and the rads need bleeding.

Chris

[Ian Chard]

I'm no expert, but I had a pressure vessel fail in a combi once, and the leaking water shorted out the not-particularly-well-waterproofed mains input. Did it sound like an electrical or mechanical pop?

- Ian

[Rednadnerb]

Thanks for the replies.

I have been reading the diy faq and found this:

'automatic air bleed unit, these devices let air out but not water, they also let air in. They work well if they only operate occasionally and are under pressure but if they draw in air they can become faulty and then fail to hold in water'

What I called the pressure relief valve is, I think, an automatic air bleed unit - a small cylinder with gnarled nut on the top. Also, the fuse in the socket on the wall is blown.

The boiler is about 10 years old. The pop didn't sound electrical but I could be wrong. The water doesn't look like it splashed the electrics but again I could be wrong.

The pressure reduced to zero and the leaking stopped after I bled a radiator.

Plan of action: replace the fuse and the air bleed unit. Fill up, stand well back and switch on. I will let you know what happens.

Again, many thanks.

[Rednadnerb]

OK, I've done that and switched on, still no lights on the boiler. Took the lid off of the circuit board box and found a glass fuse which had also blown, replaced this with a spare which had thoughtfully been provided and switched on. The glass fuse blew, that was the original sounding pop.

So I suppose I will give it all a few hours to dry and then try again.

By the way, the glass fuse says 1630L 250v, how does that translate to amps?

[Andrew Gabriel]

I think you need to find where it tracked across. There may now be a conducting layer and/or other damage.

I think you misread it. 1.6A or 630mA are plausible values, but you need to recheck. Look at the stamping on the other end too.

[Rednadnerb]

Yes, on closer inspection it was 1.6A.

Tried the second and unfortunately last fuse this morning when surely it must have had time to dry and it too blew.

This business of tracking is a bit beyond my DIY skills. I can use a multimeter to test batteries and fuses but not much more.

Could I just replace the circuit board? or could tracking occur elsewhere in the boiler, or could the short circuit be somewhere else?

[Andrew Gabriel]

Try and work out where the water will have got to. Certainly possible the fault is not on the circuit board (I might have tried unplugging everything external from the board before trying another fuse, but I haven't seen the inside of your boiler.)

Not sure if Geoff is around at the moment, but you could try

anyway for an exchange board. Somewhere like Maplin will probably have fuses, although possibly not exactly the right speed ones.

[geoff]

In message , Andrew Gabriel writes

IIRC it's printed on the pcb

also IIRC there are two fuses on the pcb - 2A and 630mA, although I can't be sure

that would be T630L - T standing for slow blow

I can check on Monday

[Rednadnerb]

Thanks Geoff but following Andrew's lead I armed myself with a box of T1.6A fuses from Maplin. Then unplugged everything from the PCB and by a process of blowing fuses traced the fault to the fan. I have no idea how this came about. The fan in not in the path of the water that was dripping from the air valve thingy. I can only assume the two faults are unconnected.

Interestingly, if I set my multimeter to beep mode (for short circuits) and connect the probes to the terminals of the fan I get no beep, just an ohms reading of about 50. If I turn the fan slowly nothing changes but if I spin it fast I get an occassional beep.

Anyway, I will have to wait to Monday now to get a new fan. Thanks for your help everyone.

[Andrew Gabriel]

Check around the fan connector on the board for water damage. An apparent double fault like this may be a less obvious cause. (Like I said, I haven't a clue what this particular boiler looks like inside, so that may or may not be a useful comment.)

Talk with Geoff about getting you a replacement fan.

[geoff]

In message , Andrew Gabriel writes

OP - was it a swiftflow 80 or 100 ?

£45 ++

[Rednadnerb]

-

Swiftflo 100. Thanks Geof but there is a local supplier close to me, Adlink in Alperton, where I can collect from. They supplied the last two, the last one just 15 months ago (mmm?)

[Rednadnerb]

Fitted the fan and switched on, fine. Lit pilot light, fine. Turned on hot tap, nothing, tried the central heating, nothing. I'd welcome any suggestions but I also think it is about time I phoned a friend.

[A.Lee]

Has this boiler got a pressure vessel that needs re-pressurising? You drain off some radiator water until the needle drops to 0, then pump up the pressure vessel to typically 1 bar, check your manual. You can use a bike pump to pressurise it. Alan.

[Rednadnerb]

No, it doesn't seem to have one of those. My friend came and went through the troubleshooting chart in the manual (something I suppose I should have done), this pointed to the main circuit board which he replaced and it is all working again. Thanks for your contributions.