Boiler breakdown and repair in London

Some faults come up again and again in south and west London homes.

Low pressure. Sealed systems should usually sit around 1 to 1.5 bar when cold, but check your boiler manual. Pressure that keeps dropping points to a leak, a failing pressure relief valve or a flat expansion vessel.

Frozen condensate pipe. Condensing boilers drain acidic water through a plastic pipe. Where it runs outside and is thin or unlagged, it can freeze in a cold snap and the boiler locks out. Pouring warm, not boiling, water along the pipe often clears it.

Ignition lockout. The boiler tries to light, fails and locks out. Causes include a gas supply problem, a blocked condensate trap, a worn electrode or a failed gas valve.

Hot water problems on combis. Hard water scale in the plate heat exchanger, a stuck diverter valve or a faulty flow sensor. Our combi boiler service page explains the scale link.

Check the gas is on at the meter and that other gas appliances work. Check the pressure gauge on the boiler. If it is low and your boiler has a filling loop, the manual explains how to top up. Check the boiler has power and the timer and thermostat are calling for heat. Reset the boiler once using the reset button.

Do not take the case off. Opening the sealed part of a gas boiler is gas work and must be done by a Gas Safe registered engineer. If the boiler keeps locking out after one reset, stop and book a visit.

If you smell gas, call the National Gas Emergency Service on 0800 111 999, turn off the gas at the meter if safe to do so, open windows and do not use switches.

Clear the area around the boiler and the gas meter. If the boiler is in a loft, check there is a safe ladder and a light. Have the manual to hand if you can find it, and note when the fault started, any codes shown and anything that happened just before, such as a power cut, a frost or recent building work. That helps the engineer find the cause faster.

Most breakdowns are fixable. Pumps, fans, diverter valves, sensors, electrodes, expansion vessels and printed circuit boards are all replaceable parts. The question comes when the boiler is old, parts are hard to get, the heat exchanger has failed, or repairs are piling up.

The engineer will give an honest view on whether a repair makes sense. If your boiler is still under a maker's warranty, check the terms first. Makers like Vaillant run their own repair service for boilers in guarantee, and a repair by someone else may affect a claim.

After a repair, get the boiler back on its yearly service. Many breakdowns, such as blocked condensate traps and worn seals, are caught at a service before they stop the boiler.

Keep a note of each repair and the date. If the same fault keeps coming back, that history helps the next engineer and helps you decide whether a repair still makes sense.