Change a micro switch and save £300

Last week three things seemingly went wrong with our central heating.

First, the boiler would need to ignite several times before the main burner came on and stayed on.

Second, the Hive control system receiver ‘lost RF’ to the hub, and,

Third, once on it would only work on hot water not the radiators.

Matters were not looking good.

So, first service the boiler, basically vacuum clean it and check all seals.

The bit that always goes wrong is the igniter and electrode. Took out electrode and discovered the lead was loose at the electrode end. I keep a spare pilot burner and electrode. The pilot burner gets corroded and unless you have a ultrasonic cleaner for the price its easier to replace both. (DHS – Direct Heating Spares)

Tested boiler on hot water only and it fired up first time every time. So boiler OK.

Next removed the Hive receiver from the wall. The base plate was cracked and the connecting pins were corroded and blackened. It may have been caused by the poor igniter system but my guess is that it was poorly installed and sealed to the wall. Utility rooms can be very damp.

Go a new receiver and commissioned it to the hub. All good with support from Hive technicians. Control systems OK

Finally the tricky bit, why didn’t the boiler heat the radiators. There is a motorised valve next to the tank. I remembered that it can be placed in manual to open the valve and sent hot water to the radiators.



What I hadn’t realised is that there is a micro-switch in the valve body that once the valve is open to allow water to flow will close the circuit to start the boiler. Not in the boiler service manual. However, this was intermittent. So, even when open the boiler didn’t always fire up.

The picture show the valve with the cover off.


A temporary loop closing the circuit in the breakout box confirmed the fault.

The good news was that although 20 years old a replacement head can be bought from ScrewFix for £50 and ready within the hour.

Replaced and rewired the head. The new colour coding was not quite the same as the old. But it was logical.



All fixed, we now have a boiler up and running for the winter. I hope…

Total cost to us under £100. Had a boiler engineer attended, cost at least £300, maybe more, plus parts? Plus the agro waiting for someone to come fix it.

Don’t try this at home. I’m an experienced engineer and if in doubt I ask for advice and help from friends in the trade. 










About Peter Block

renaissance man in training
This entry was posted in Heating systems, How to work on a central heating system, Plumbing. Bookmark the permalink.

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