Frustrating unexplained boiler problem

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30 Jun 2014
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Hoping somebody can help me understand a weird boiler issue I had this weekend.

I'm in the process of converting a cellar, and as part of this I needed to raise all the central heating pipes into the floor joists above as they were hanging down. (Basically just shifting them so I could put the cellar ceiling in.)

I drained down the system, and spent all day moving the pipes. (One thing I did, which I think was a stupid mistake, was to leave the water on so the kids could have a shower. With hindsight, and some googling, looks like it's a bad idea to run hot water with the CH drained.)

After I'd shifted the pipework I re-pressurised the system, but found the boiler (Worcester Junior 28i) wouldn't fire. Was just getting a flashing red light. (No pump noise, sound of ignition - just silence and a flashing light.) Tried resetting it, checked the fuses, powered off at mains for 10 mins - but still no hot water. This is when I started Googling, and assumed I'd fried something when I ran the hot water - my guess was the PCB.

After being heavily berated by my wife I admitted defeat, decided it was beyond me to fix, and called out British Gas.

Fast forward to Sunday morning. I noticed there was a slight drip from one of my joints (soldering too close to a bend!) so I re-drained the system, re-joined where the leaky fitting was, and re-pressurised.

Couple of hours later while waiting for British Gas to come out I thought I'd try the reset again - dunno why. Anyway - boiler fired fine, hot water works, CH works fine too.

Cancelled British Gas to save myself a call-out charge, but now this is really niggling cos I can't figure out the cause.

Can't have been overheating, because the boiler was down for 6 hours unable to reset. Can't have been a fried component, because it would have stayed fried. It seems that it was draining / repressurising a second time that sorted it.

I can't believe it was one leaky joint that stopped it firing. (It was a drip every couple of seconds.) Only thing I can think is an air bubble or something.

Anyone shed any light on this? It's driving me mad!
 
You may well have seized up and overheated the pump.

After cooling and a few days it could have restarted.

Tony
 
Cheers Tony. I initially thought overheating was likely, but thought 6 hours would have got it as cool as it was going to get. Could it take longer than that?
 
After seizing up it would take extra torque to start it turning.

Repeatedly trying can eventually get it started.

There are temperature and corrosion effects involved and so not a totally linear situation.

Tony
 
Thanks Tony - that makes more sense now. I guess my lesson learned is not to run the hot water with the CH system drained!
 

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