Cold radiators (hot boiler)
If your boiler is working but some radiators are cold, the most common cause is air trapped in the radiator. Bleed the radiator using a radiator key (turn anti-clockwise until air hisses out, then close when water appears). If this does not solve it, the system may need balancing — a heating engineer adjusts the flow to each radiator to distribute heat evenly.
Boiler pressure drops
Most combination boilers should operate between 1–2 bar pressure. If the pressure gauge regularly drops below 1 bar, there is a leak in the system or the expansion vessel has failed. Top up the pressure via the filling loop (the braided hose under the boiler) to 1.5 bar. If it drops again within days, call a Gas Safe engineer.
Noisy radiators or pipes
A banging or ticking sound from radiators or pipes is often caused by a build-up of sludge (magnetite). Over time, rust and debris accumulate in the system, reducing efficiency and causing noise. A power flush (£300–£600) removes this sludge. Adding inhibitor to the system prevents recurrence.
Boiler keeps locking out
A boiler that repeatedly fires and then locks out (displays an error code) needs investigation by a Gas Safe engineer. Common causes include low pressure, a faulty pump, a blocked condensate pipe (in freezing weather), or a failing PCB. Do not continue to reset a locking-out boiler without finding the cause.