New wall socket for dishwasher blows power to boiler?!


Postby Jpsmythe » Fri Aug 26, 2016 9:48 pm

Hi! Apologies for my lack of knowledge about this, and sorry if my use of terms is wrong in advance. I'll try and explain as best I can!

A few days ago, a handyman fitted a new plug socket in our kitchen so that we could install a brand new dishwasher. Dishwasher arrived today, plugged in and set up by the delivery guys, all worked fine. Twenty minutes into the dishwasher cycle, it turned off. There was no power coming from the socket the guy installed. I tried the dishwasher in another socket, worked fine.

So I assumed that socket isn't working okay. But then also: at exactly the same time, our combi boiler has stopped working. No power to it or the thermostat. It's a few rooms away from the kitchen. Those are the only things not working, and nothing has tripped in the fuse cupboard.

I've tried resetting all the fuses but can't get the boiler started. I've spoken to the handyman who says it can't be related, that he checked the plug socket twice etc, and he's going to come and look at it, but I wanted to see if anybody had any opinions on this before he came - mainly because we now have a useless new plug socket and a boiler that I can't turn on at all. I don't know how circuits work, don't know much about fuses. But I don't want to get ripped off here if he claims it's not his fault, if it very clearly is etc.

Hope that makes sense. Any advice much appreciated!
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Postby ericmark » Sat Aug 27, 2016 10:09 am

I will guess that the boiler is protected with a fused connection unit (FCU) and the handy man has taken the supply from this and the fuse likely 3A has blown as not big enough for a dish washer but it is big enough for a boiler.

He should have issued a minor works certificate when he did the work which should detail what he has done and what reading he got when he tested it. Although fitting a socket seems easy, the first part of the job is to find a supply.

We have to be careful not to take a spur from a spur, A house normally has either a ring final or a radial final system, it can have 2.5mm sq or 4mm sq cable, When extending we have to ensure the volt drop is within limits, and that if there is a short circuit the protective device will trip within the required time. To do this we use a loop impedance meter, once fitted we then retest and also use a RCD tester to ensure the RCD does not trip with a 15 mA fault and does trip with a 30 mA fault and it trips in 40 mS. There is a third meter also used, these meters cost around £750, but the scheme provider who registers electricians and allows them to issue compliance certificates require them to have these meter.

Depending on where he took supply from, and what room it was in, and if in England, Wales or Scotland, he may not need to issue a compliance certificate. However he should still issue a minor works certificate which will record the reading he got, and listing what he did.

Look for a socket sized box with a fuse in it, I will expect you will find a 3A fuse which when replaced the boiler will work, and if you use dish washer again it will blow the 3A fuse, do NOT let him replace with a 13A fuse, as that will be too big for the boiler.
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Postby kbrownie » Sat Aug 27, 2016 10:35 am

Does not sound like the handyman has the relevant skill set to install a socket!
Did you get any documents with test results for this work and proof it was safe to use, it is a legal requirement that all domestic electrical work complies to part p of the building regulations.

As Eric has pointed out, it is possible that the unhandyman has installed the socket via the load side of boiler's FCU. And overloaded the fuse.
Or it could be possible that the circuit is a radial or spurred spur, and a wire has become loose/broken or another upstream fuse has blown, that has given power loss to both boiler and WM socket.

Is there any RCD protection on this circuit?
If not the unhandyman should have installed it, and that could also be a factor of both appliances not working.
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