Fault finding

[Colin Freelove]

Can anyone help me with this problem ? Below the timmer control and switches to my boiler is another small light switch type switch with a fuse in it. The mains seems to run into this switch then on to the control panel. My first question is what size of fuse should be in this switch, and secondly when I stand in a certain place on the landing this causes the house trip to activate, it would seem there is a wire too close to floor boards which when pressure is applied it throws the trip. This seems to be the same wire that leeds to boiler switch. Can anyone help with advice, money is tight at this time. Thankyou

[Martin]

My boiler is fused at 3A.

You will have to take up the floorboards to investigate the tripping fault, something under there is shorting out.

Martin.

[Lurch]

A 3A fuse is always used for heating systems.

Sounds likely, best bet would be whip the boards up and (carefully) find which wire under there is faulty. Hopefully it should be fairly obvious which one is trapped, or possibly caught by a nail from the floorboard. When you find it either repair the faulty piece with a junction box, or replace the length of cable altogether. It all depends where the cable runs I suppose as to which way you do it.

A.C.S. Ltd.

[geoff]

In message , Lurch writes

Not necessarily.

There are a number of boilers which have 4A fuses on the pcb,

[M. Damerell]

[snip]

If there is a nail through the cable, I suggest that you turn off at the mains before trying to pull it.

[Lurch]

That there may be, but no-one mentioned PCB fuses. Perhaps should have said, 90% of heating systems use a 3A fuse, in the unlikely event you have a commercially rated heating system check the manufacturers details. ..

SJW A.C.S. Ltd.

[geoff]

The fuse on the pcb comes after the main boiler fuse, fuses are there to protect the wiring, so what's the point of a larger fuse on a subset of the whole system? The Halstead quattro ignition pcb (which basically operates the GVs and creates the spark) has a 4 fuse on it.

The fuse on the pcb is a slower blow fuse than the main fuse (no idea what the main fuse rating on this boiler is)

I'm not talking about commercial boilers here, it would shoot up drastically if I did

[Lurch]

I was going to say it's probably a fast blow fuse, until I got to this bit.

You sure the 4A fuse is on the 240V side? ..

SJW A.C.S. Ltd.

[geoff]

In message , Lurch writes

Having repaired one yesterday, I can categorically say it is.

As I said this is not an isolated case. Not common, but they do exist

[Lurch]

Interesting, I haven't come across a boiler, other than in schools etc, that dont say in the instructions use a 3A fuse. Having said that I've just recently wired up 2 huge boilers in a leisure centre, 3A fuses to each one as per manufacturers spec. ..

SJW A.C.S. Ltd.

[Martin Angove]

Could it be one of those discrimination things? The 4A on the PCB is there as a "last resort". In theory in a fault condition the 3A should blow first, and as this is on the "customer" side of the installation, it should be easy to fix, and it's a standard BS 1363 fuse too which is dirt cheap. Perhaps a DIY-er has replaced the valve and misplaced a wire. If the 3A blows it is relatively easy for him to realise what has happened, trace and fix the fault and replace the fuse. If the PCB fuse goes first most DIY-ers would give up and call someone who knows about boilers.

The 4A is there to be a "non fiddlable" item which protects the electronics if said DIY-er is completely stupid and sticks a 13A fuse on his side of things or even wires it up straight to a 16A radial or a non-fused spur on the ring.

After all, whatever the instructions say, the boiler manufacturers can't be there to ensure everything is fitted as per the instructions, and surely it's better to have the PCB fuse blow than to blow a few tracks and components, thus requiring a new PCB?

Just a thought...

Hwyl!

M.

[geoff]

In message , Lurch writes

FFS, do you take me for a moron ?

[Lurch]

I do now. unless you were in tongue in cheek mode. ..

SJW A.C.S. Ltd.

[geoff]

Well, I see it as a fairly silly question to ask someone whose business is repairing pcbs for boilers