Strange electrical problem

[ScottishGasMan]

Quite some time ago, I was working on a boiler that had a very intermittent fault, many people had been out before and it was working ok,

When I went out the fault was their, so I proceed to do my electrical checks on it to find reversed polarity. I thought to myself thats a joke this should have been sorted on the first visit.

I checked the sockets in the house and found the same. I phone an electrician that worked for us at them time (cant remember how we got to this point) but he told me to plug my meter (simple socket and see loop tester) into the wall and start isolating circuits at the fuse box, eventually I isolated the downstairs lights and suddenly the socket and see was flashing all green indicating all was well.

Fired the boiler up and it ran away fine. So I turned all lights off, and restored power to lighting circuit all ok. turned the lights on one at a time till I hit the living room light, it came on and worked fine, but sent the socket and see (that was still plugged into the wall) mental and the boiler started flaking out.

To which the customer told me her ex-man wired that light in a few months back, and being that it had been summer neither the light or boiler had been on much.

So she was told to get an electrician to get a look at it and never heard back.



My question is, what mismatch of wiring could have caused that without blowing a fuse etc?

 

[ban-all-sheds]

My question is why should a boiler act up when connected reversed polarity?

 

[ScottishGasMan]

Well I know they do, Ive had a few do it.

They use the earth for flame rectification, Where your ignition unit uses an AC signal to make the spark, then when flame lights a very small DC current will be bridged over the flame between the electrode->flame->earth. This seems to get upset on some with reversed polarity. (dont actualy know why)

Modern boilers and their controls seem to be about the most sensitive thing to electrical faults in a house.

 

[Spark123]

Could be a TT earthing system without a working RCD on all circuits, a L-E fault on the lighting circuit causing what appears to be a reverse polarity.

Equally could be a system without an earth or an open circuit earth on a TN system. Definitely needs attention, if it is a TT supply an electrician is required. If it is a problem with a suppliers earth then over to the DNO.

What you are probably measuring (with respect to true earth) is all the ECPs live at 230v, the live at 230v and the neutral at 0v.
L-E = 0v
L-N = 230v
N-E = 230v

As L-E should be 230v and N-E should be 0v it shows up as reverse polarity.

 

[matt1e]

My question is why should a boiler act up when connected reversed polarity?

You'd be surprised, many do, it boils down to ignition and sensing
The majority of modern boilers detect reverse polarity these days anyway and give an error code

Matt

 

[Lectrician]

I would say that there is a dodgy earth to the building (non existent or high resistance), or a TT install with dodgy RCD or old school ELCB. This coupled with a L to E fault on the lounge light.

Some boilers don't like reverse polarity at all - Seen it a few times.

I wired a fairly complex heating system a few years a go on a new build, and the plumber decided he was going to fire it all up without consulting me. He disconnected the FCU and put a flex directly into the FCU with terminal blocks, and plugged this into an extension he had made himself (a metal clad socket on the end of the some flex).

He had a right strop at me saying the controls must be wired in reverse polarity as to get the boiler to fire he had to swap the polarity around in the boiler.

You cannot exactly get the polarity wrong doing control wiring, so I went straight to his extension and found that was reverse polarity! The extension HE had made.

After the grief he had given me, I gave him plenty back, and we never had a good working relationship after, until he retired! He was a complete tosser of a plumber. He should never have fired up MY control wiring anyway.

This is the same plumber who cause issues on a job because I had done the MPB to the gas in the garage where it came through the wall and not in the gas meter box, wound a customer up by asking where the bonding for the kitchen sink was on a new build, and commented to a customer about the lack of fuse on an immersion heater circuit where I had used a DP switch on the end of a 16amp circuit rather than an FCU (which is the correct way to do it!).

I was not sad to see him go - It was unfortunate that out paths kept crossing! I used to turn up on jobs, see his van and groan.