Intermittent Boiler Issue

[waddycall]

Had a similar issue with a customer who thought their boiler was tripping the RCD. Couldn’t find anything wrong with it and it rarely tripped when I was there. One of our sparkys went to have a look and found it was accumulated earth leakage mainly caused by the washing machine. Every now and then the boiler would put it over the limit.

 

[mtt.tr]

Had a similar issue with a customer who thought their boiler was tripping the RCD. Couldn’t find anything wrong with it and it rarely tripped when I was there. One of our sparkys went to have a look and found it was accumulated earth leakage mainly caused by the washing machine. Every now and then the boiler would put it over the limit.

Yes low range clamp meters are great for this, actually the reason i own one

 

[tommullin]

Had a similar issue with a customer who thought their boiler was tripping the RCD. Couldn’t find anything wrong with it and it rarely tripped when I was there. One of our sparkys went to have a look and found it was accumulated earth leakage mainly caused by the washing machine. Every now and then the boiler would put it over the limit.

washing machine or anything else (significant) wasn’t running at the time, I was at work...

could a faulty appliance like that cause a symptom like this? while it’s on but not running, in standby mode (eg washing machine/vacuum)?

or should I keep looking at the boiler as the culprit?

 

[dobbslc]

Yes an earth/neutral fault can trip an RCD even when the item is switched off.

 

[hunter27]

Have a good look around for a slight water leakage near or above any electrics or wiring on the c/h system, even if you don't see anything wet a leak will usually leaves an obvious residue.

 

[gaz1]

id also suspect a jamming pump on the boiler

how long have you had the boiler

what boiler make is it

 

[tommullin]

Yes an earth/neutral fault can trip an RCD even when the item is switched off.

interesting.

when this happens, I can trip the global rcd every time I connect the downstairs sockets with the boiler on. Or, I can trip it by just switching the fused spur for the boiler. But... that doesn’t mean it’s not a combined leakage if stuff can leak even when it’s off. There’s a lot more stuff on that circuit that could be contributing!

thanks again everyone, loads to think about

 

[Martinb]

Put boiler on its own rcbo and try that?

 

[dobbslc]

It'll still be running through the master rcd though ^
If you,want to be certain it's the boiler you'll have to turn off everything else AND disconnect all the other neutrals except the boiler and then see if it still trips. As @Kayos says if that model has trouble with the board it might be worth a look at to see if it's got any obvious damage.

 

[dobbslc]

Try these guys if you need a circuit board. I've used them before and they are good.
https://www.cetltd.com

 

[waddycall]

washing machine or anything else (significant) wasn’t running at the time, I was at work...

could a faulty appliance like that cause a symptom like this? while it’s on but not running, in standby mode (eg washing machine/vacuum)?

or should I keep looking at the boiler as the culprit?

The washing machine on our job was causing problems when it was off. Customer was convinced it was the boiler. Glad I didn’t fit any new parts to it.

 

[voipio]

Is there any trace of a weep e.g. from the heat exchanger, or possibly from condensation? Humidity is vvv high at the moment, so it won't take much.

 

[hunter27]

In my very limited experience water has causes most of our problems. Usually kettles, steam irons or the dish washer getting damp where they shouldn't then drying out.

 

[tommullin]

just a quick update, I had a look around the boiler and nothing looks bad, but the old economy7 (emersion heater) is still wired in and just powered off. The pump for that doesn't look great, so I think next time this happens i'll try disconnecting just the e7 stuff and see if its that or something else on the system.

thanks again for the replies, some decent suggestions!

 

[WorkshopChris]

Yes an earth/neutral fault can trip an RCD even when the item is switched off.

I want to scream when I find someone has fitted a cheap single pole switched fuse connection.

 

[tommullin]

Hi Guys,

thanks for all the replies and advice on this, I forgot to update the thread.

I went away for about a month, came home to a very cold house just before Christmas and the boiler was kaput. The house was pretty cold, so I'm guessing the boiler tripped the RCD and took the whole house out not long after I left.

Turned out you guys were right in the first few replies (@brightspark and @Kayos etc); it was the water pump. Confirmed by testing the resistance of the motor and seeing it was way out of spec, and resolved by replacing it.

I did make a few mistakes.

• I kept trying to run it (thinking id only trip the RCD), and blew the boiler fuse.
• I replaced the boiler fuse and blew the replicable fuse on the board
• I replaced the replicable fuse on the board and blew the board!!!

Luckily, I blew a 'zero Ohm resistor' so it was an easy fix, along with a £20 almost brand new identical pump.

Anyway, just an update to say thank you to everyone who helped and to add the solution so anyone who searches (or just observes) knows the outcome and symptoms.

 

[gaz1]

your lucky that you didnt loose the whole pcb board many peopel do who dont have an electronic knowledge of pcb boards and have to replace an expensive part in them

 

[tommullin]

your lucky that you didnt loose the whole pcb board many peopel do who dont have an electronic knowledge of pcb boards and have to replace an expensive part in them

I sure was lucky, the zero ohm resistor was obliterated, and finding a circuit diagram wasn't easy. I managed to find an eBay advert for a board with a picture with enough resolution so I could see the '0' on the component. I didn't get to give him a 5* rating as I didn't pay the £300 odd!!!... I came bloody close though!

 

[dobbslc]

Glad you got it sorted.
If anyone needs a boiler PCB or other bits these guys do refurbished ones for a decent price.
https://www.google.com/url?sa=t&sou...FjANegQIBxAB&usg=AOvVaw0RDC3NX60h54mvvXCMzXiW
I assume they're shut at the minute due to Corona and will reopen....