Nearly every heating fault gets reported as a boiler fault. A good number of them are not. The boiler is the loudest part of the system and the only part with a display on the front, so it takes the blame for pumps, valves, controls, wiring and water nobody has looked at in years.

The system is longer than the boiler

Between the boiler firing and a room getting warm there is a pump, a diverter or motorised valve, a programmer, a room thermostat and its wiring, the valves on each radiator, an expansion vessel and the water itself. A fault anywhere along that chain arrives as the same complaint, no heat, and those parts are nothing like each other in price. Working out which link has stopped is the job.

How we work back through it

• Is a demand reaching the boiler at all? Programmer, room thermostat and wiring come first.

• Does it fire and drop out, or never fire? That separates ignition and sensing faults from control faults.

• Is water moving? Flow and return temperatures show whether the pump is shifting anything.

• Is the demand going where it should? Valves are the usual reason for hot water and cold radiators, or the reverse.

• Is pressure holding? If not, water is leaving the system or the expansion vessel has lost its charge.

• What does the water look like? Black water explains repeat failures better than any fault code.

When the system is the fault, not the part

A pump that seizes twice, a valve that goes again, radiators cold along the bottom, air that keeps coming back — that is not bad luck with parts. Corrosion debris circulating around a system wears pumps and valves and blocks the narrow passages in a modern heat exchanger. Fitting the same part again treats the symptom. A magnetic filter on the return does more for a system than an oversized pump will.

Repair or replace

Repair is the sensible call on a boiler that is not especially old with a part still in production. Replacement makes more sense when parts are obsolete, when there have been several separate failures, or when the fault is a heat exchanger, because at that point you are spending a large share of a new boiler on an old one. We will tell you plainly which you are in. New boilers start at £1,900 + VAT supplied and fitted for a straight combi swap, same type and position, including the boiler, flue, fittings and a system filter.

We work on Worcester Bosch, Baxi, Vaillant, Ideal and Glow-worm. Fixed price agreed before work starts, no call-out fee. Call 0161 515 9977 or email admin@nelsonplumbing.co.uk.

Common questions

The boiler is showing a fault code. Does that not tell you what is wrong?

It tells us what the boiler noticed, not why it happened. A low pressure code means pressure is low, which could be a leak on pipework three rooms away or an expansion vessel that has lost its charge. A no-flow code often points at the pump or a blockage rather than at the boiler. The code narrows the search down. It is not the diagnosis.

Why test the whole system when only one thing is broken?

Because the symptom rarely sits where the fault is. Cold radiators with plenty of hot water can be a valve, a pump or a control, and those are very different bills. Checking the chain in order takes a little more work than swapping the obvious part, and it is the difference between fixing it once and paying for two visits.

The same part has failed twice in a year. Is that bad luck?

Usually not. A part failing repeatedly is normally being killed by something else: most often debris in the system water grinding through pumps and valves, sometimes a pressure fault putting a component under stress it was never designed to take. We would rather find the cause than sell you the same part a third time.