When delving into the control box of my heating sytem to replace the fuse on the PCB, I stupidly had not checked the power was off and shorted something out aginst the metal casing. There was a loud 'pop' and a flash, I'm probably lucky to be here still.

The fuse was still out of the system at that stage, and the only other thing on the PCB seems to be this relay. It doesn't look burnt out at all, but there is not much else that could have blown. Can you tell when a relay has gone by looking at it? This is a 14-pin job. How can you check it out.

It may be difficult to find one, so I don't want to go through the effort that is not the problem.

Thanks fr any advice received.

Tongalad, April 2009

Thanks for the reply Peccavi.

I'm not really intending to try and mend anything, just get the heating working as quickly a possible.

It is a Baxi Bermuda 551 (very old) back boiler which is a long way away from the wiring box in which the PCB sits which the fuse and relay sit in. Is this PCB likely to be standard for the boiler then?

I think I foolishly shorted the live feed to the metal casing, so I guess it could be anything that went pop. Possibly even the Randall control unit, which does show the signs of a scorch mark.

Thanks for advice anyway.

Tongalad, April 2009

You don't mention the boiler make or model?

You can not usually tell if a relay is defective by looking at it

Relays are relatively inexpensive from a component supplier as low as £2 possibly up to £5 depending - it will likely be a bog-standard low price relay unless there were no cost constraints placed on the designers.

Relays are relatively easy to diagnose - can you hear it switch over when it's energised is the first test - this is best done on a bench with a power supply and a circuit diagram which you are unlikely to have.

You say apart from the fuse the only other thing on the PCB "seems" to be the relay - and that's a little unusual - a designer will not design in a special PCB with just a fuse and a relay unless it's for a modification of some sort.

A 14 pin relay suggests 2 contacts for the energising coil and four Double Throw switches each with three pins, which is a bit complex. There will hopefully be numbers on top - put them into google and see what comes up.

If money rather than time is a problem then attempt a component repair but it's difficult without a circuit diagram.

If time is the issue and you need a quick fix then invest in a replacement PCB and fix the old one at your leisure.

Good luck...

Peccavi, April 2009