Replacing the Thermocouple on a Baxi 51/3RS Boiler

14 Jul

So, the other day, the missus goes to take a shower and then quickly realises that there is no hot water. I checked the boiler and the pilot light had gone out, damn it, “oh well, I’ll just relight it” I thought. Which I did and then the next morning, no hot water again. This time though, it wouldn’t stay lit, no matter how long I held the little green button in place, it just kept going out.

We tried a few local boiler repair chaps but they were all fully booked for the weekend and I had a bit of free time so I thought I’d investigate further. After a little bit of reading on various forums, it soon became apparent that I needed to find out what a thermocouple was; everybody was going on about them.

Turns out its a relatively simple part, that sits in the pilot flame and produces a very small electrical current when heated. It’s pretty much a safety feature so your house doesn’t fill up with gas if the pilot light goes out. With my hand on the green button and the pilot lit, I used a volt meter to measure the current at the other end, I was getting nothing at all which suggested that it was this part that was knackered. Best of all, it a very cheap part so I got straight on the bay.

Now, I like to think of myself as a bit of a handyman, I’ve done the odd bit of this, a bit of that, but I’m no boiler expert. In fact, legal bit here, I’m not responsible if you blow up your house, ok?  And the boiler when you think about it is a nice mix of water, gas and electricity. Either one on their own could cause a lot of damage, mix them all together and the results could be pretty spectacular. So, basically I wasn’t going to attempt to fit a new boiler by myself, but replacing the thermocouple seemed like a job anyone could do, even if they’re not supposed to, ahem.

Our boiler is a Baxi 51/3RS, it’s pretty old by all accounts, and replacing it was going to be a lot more expensive than I had anticipated, so I was really hoping that I could repair it! Anyway, I just searched on the bay for “Baxi Thermocouple” and got one brand new, delivered for four English pounds, bargain.

It really is a doddle to fit, unscrew the old one and both ends and screw in the new one, job done. All that was left to do was test it, and hey presto when I let go of the green button, the pilot light stayed on. Total spent: £4.00. Not £400 to repair or even more to replace. Fingers crossed that it keeps going for a little while longer.