Kingfisher thermocouple
Today I fixed a Potterton Kingfisher by replacing the thermocouple. The Kingfisher is a really basic and super-reliable floor-standing gas boiler from the 1980s. There are plenty still in regular use today. The pilot flame on this one kept going out, needing repeatedly re-lighting.
The most troublesome thing on a Kingfisher is the pilot light. It sometimes goes out and needs re-lighting. If it won’t re-light then the component called a “thermocouple” probably needs replacing, and that is what I did today. Replaced one I mean.
This particular Kingfisher was noteworthy for the poor access. It was tucked into a corner with only about a foot or so of free space in front of it. Normally I’d say there needs to be three feet of clear space in front of the boiler to work on it but in this case I was still able to remove the burner assembly to get at the thermocouple. Here are a few photos I took on the way.
The thermocouple is a little metal rod which heats up in the pilot flame and produces a small electrical current, which keeps gas ON all the time there is heat from the pilot flame. If the flame goes out for any reason, the thermocouple cools down, the electrical current stops and the gas gets turned off. It’s a safety device to stop the flow of gas if the pilot flame goes out. With the passage of time the flame eventually burns through the outer casing and damages the actual thermocouple inside, as you can hopefully see in the photo on the right.
This photo shows the new thermocouple tip in position, with the burner assembly cleaned up and ready to be re-fitted into the boiler.
I keep ‘universal’ thermocouples in the van and it is a straightforward job to fit one normally, taking about an hour to replace one and service the boiler at the same time. Very little else goes wrong with the Potterton Kingfisher.
Here are the two thermocouples, the old and the new, lying next to each other on the dust sheet. Zoom in and you’ll easily see the flame erosion on the old one!
Occasionally I’ll attend a Kingfisher with a pilot flame that won’t stay alight and replacing the thermocouple makes no difference – the pilot flame still won’t stay alight. This can happen if the pilot flame is too small to properly envelope the thermocouple tip, or if the coil inside the gas control valve has failed.
The Kingfisher is a well-regarded old format boiler but gets criticised for poor fuel efficiency. It is approx 65% fuel efficient (varies slightly according to the exact model). This figure of 65% means the boiler extracts 65% the energy in the gas it is burning in useful heat for radiators and hot water, and the remaining 35% gets lost or wasted to outside, via the flue gases. A modern boiler will be about 90% fuel efficient or a little better so fuel bills will be lower, but the Kingfisher wins out in terms of reliability. Fewer breakdowns than a typical modern boiler, and cheaper to fix if it does go wrong.
I’ve written more about the Kingfisher on my main website here:
https://www.miketheboilerman.com/potterton-kingfisher.html