Intermittent Boiler Issue

[tommullin]

Hi guys,

I appear to have a very intermittent issue with my boiler. I have tried absolutely nothing and I’m all out of ideas. Honestly, I just thought someone might know some likely culprits I should check first before I get too deep down rabbit holes.

So I have only one rcd protecting every circuit, so if it trips, I have to drink warm beer and have a cold shower. I know it’s the boiler that’s causing the trip as that’s the thing that trips the rcd when I turn everything back on individually.

the rcd has tripped twice in the past few weeks (both times it was the boiler) and both times it wouldn’t reset for about an hour, then worked fine. After failing to reset a number of times (rcd kept breaking), waiting for about an hour and trying again, it all worked OK.

I was away in Australia for about a year and this never happened - I left the heating and water on low heat. I did have the same issue before I left, but it’s only started again since I’m back. I have increased the water and heating temp since I’m back.

I’m going to guess at a pump. But does anyone have any clues on where to start looking? I’m 17th edition and not an idiot, but not massively clued up on central heating systems. It’s an old glow worm micron system with a hot water tank and a switched off at the cu economy7 if that makes a difference?

thanks in advance!

 

[brightspark]

obviously earth leakage so an insulation tester is needed .

 

[Kayos]

Glow worm micron suffers from melting pcb issue, but most likely culprit is pump, or fan, or diverter valve or a wiring fault

I'd get a heating engineer in

 

[tommullin]

Thanks for the quick reply BrightSpark...

so a megger, cut the supply and start chopping the circuit up and testing parts to zero in on the fault?

I’m guessing I can’t megger the controller, motor, or anything else other than cable. So just bell out the cables and test? How would I check the pumps or is it ok to test them at 500v?

 

[Seadog]

Does it trip the moment you reconnect or when heat is demanded?

 

[tommullin]

Jesus. 6 minutes and I get brightspark and kayos?!? I was hoping one of you two might see this!

kayos - pcb is more my field. Thanks for the heads up. I’ll take a look.

thanks again guys!

 

[brightspark]

your checking live earth or neutral earth not across live and neutral test at 240v 1st then 500 its only electronic parts that are liable for damage like sky tv freeview or sensitive stuff that don't like power surges . pumps motors clocks and valves are not a problem .

 

[tommullin]

Does it trip the moment you reconnect or when heat is demanded?

it’s as soon as I reconnect that circuit, or specifically that appliance. Well, maybe nearly a second? I’ll record it next time.

 

[Seadog]

In which case, if the boiler is powered off, that should preclude the pump and the fan.

 

[tommullin]

your checking live earth or neutral earth not across live and neutral test at 240v 1st then 500 its only electronic parts that are liable for damage like sky tv freeview or sensitive stuff that don't like power surges . pumps motors clocks and valves are not a problem .

thanks bs. Good info. So the correct procedure is to isolate that circuit and test L-E & N-E, then home in on the problem area / device?

 

[tommullin]

In which case, if the boiler is powered off, that should preclude the pump and the fan.

Pump/fan would make sense to me. As it fixes itself. But I’m not sure if it fires the pump/fan on power up. I’ll check.

thanks seadog. Any suggestions of cheap components are welcomed

 

[the snooper]

Disconnect pump and try it, then fan, then diverter valve you'll soon find the culprit

 

[tommullin]

Disconnect pump and try it, then fan, then diverter valve you'll soon find the culprit

good plan. Only problem is it’s intermittent and fixes itself quickly. I’ll make a plan so I can action this procedure quickly if I catch it in fault condition again. No problems with running the system with these components disabled? I will only need to do it briefly.

 

[brightspark]

part all the neutrals then test individual switched live feeds independently then you wont get any back feeding readings

 

[tommullin]

part all the neutrals then test individual switched live feeds indipendently

cheers BS, I’ll research exact procedures. Good to know from a pro that you know isn’t an idiot that you’re going down a good path!

really appreciate all the advice guys.

 

[WorkshopChris]

Does it still trip the RCD with everything else in the Consumer unit off?
One possibility is existing equipment with leakage just under the tripping level of the rcd then one more appliance turns on and trips the rcd.

 

[tommullin]

Does it still trip the RCD with everything else in the Consumer unit off?
One possibility is existing equipment with leakage just under the tripping level of the rcd then one more appliance turns on and trips the rcd.

Hi Chris,

yeah I did this test first time. It’s not load dependant, the fused spur for the boiler or the mcb for the downstairs socket circuit alone trips the global rcd. But good shout and thanks for the input mate!

 

[WorkshopChris]

Hi Chris,

yeah I did this test first time. It’s not load dependant, the fused spur for the boiler or the mcb for the downstairs socket circuit alone trips the global rcd. But good shout and thanks for the input mate!

That's good glad you ruled it out, have seen it before.
Had one on a lager old motor VFD, a customer was convinced it was faulty as every time it was powered up the RCD tripped, upon testing it was ok but lots of other leaky bits all hanging off the same RCD they blamed the last one to be powered up and put the RCD past its limit.

 

[tommullin]

That's good glad you ruled it out, have seen it before.
Had one on a lager old motor VFD, a customer was convinced it was faulty as every time it was powered up the RCD tripped, upon testing it was ok but lots of other leaky bits all hanging off the same RCD they blamed the last one to be powered up and put the RCD past its limit.

that would explain why it didn’t happen for a year while I was out of the country and no load on anything else (except computer/network/internet stuff).

to be honest I was expecting something like that, but I can only think that it’s happening now because the water/heating temperature is set higher. Although I’m not sure why that would happen? Maybe higher pressure causing a leak in a pump? Or thermal expansion in a fan/pump?

this forum is ace! Thanks guys!

 

[octo0072000]

Change RCD if it's old ?