How can you tell a relay is blown?

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