What 20 Years of Boiler Diagnostics Has Taught Me

After more than 20 years working on boilers, heating systems, cylinders, controls, and heat pumps, I’ve learned that successful fault finding is not about replacing parts. It’s about understanding how the system works and following a logical process.

One of the biggest mistakes I see is replacing parts before carrying out proper testing. A boiler stops working and someone assumes the PCB has failed. The heating isn’t working and the pump gets replaced. Hot water stops and a motorised valve is fitted.

Over the years I have learned that the symptom is rarely the actual fault.

A customer might tell me their boiler keeps losing pressure. The pressure loss could be caused by a failed expansion vessel, a faulty pressure relief valve, a hidden leak on the heating system, or another component entirely. The pressure loss is only the symptom. The real job is finding the root cause.

This is why good diagnostics matter.

Many of the breakdowns I attend have already had parts replaced before I arrive. Unfortunately, replacing parts without a diagnosis can become expensive very quickly. The cheapest repair is often not the engineer with the lowest price. The cheapest repair is usually the one that identifies the fault correctly the first time.

Good fault finding saves money, reduces repeat visits, prevents unnecessary parts being fitted, and gets the heating system back up and running.