A boiler that repeatedly loses pressure is telling you that water is escaping from your sealed heating system somewhere, or that a component such as the expansion vessel is not doing its job. We diagnose pressure loss issues across Cheam and Sutton.
A one-off drop in pressure, for example after bleeding a radiator, is normal and easily fixed by repressurising via the filling loop. Repeated pressure loss over days or weeks is different and usually means there is a leak somewhere in the system, or a fault with the expansion vessel or pressure relief valve.
Because the leak causing pressure loss is not always visible, especially if it is small or hidden under a floor, an engineer will check the whole system rather than just the boiler itself.
Common causes of repeated pressure loss
- A small leak at a radiator valve, joint or pipe connection
- A faulty pressure relief valve discharging water
- A failed expansion vessel not absorbing pressure changes correctly
- A leak inside the boiler itself, for example at the heat exchanger
- An automatic filling loop faulty or left slightly open
What an engineer checks
An engineer will check for visible leaks around radiators and pipework, check whether the pressure relief valve is discharging (often visible as a pipe dripping outside), test the expansion vessel's pre-charge, and inspect the boiler itself for internal leaks.
The expansion vessel
This component absorbs the expansion of water as it heats up. If its internal pressure is wrong, the boiler can lose pressure repeatedly even without an external leak.
What you can check yourself
Check around visible radiator valves and pipework for damp patches, and check whether there is a pipe outside your property, often near the boiler flue, that shows signs of dripping, which would indicate the pressure relief valve is discharging.
How charging works
Diagnosing and repairing pressure loss is charged by time at our standard hourly rate, plus parts such as an expansion vessel or valve seals. See /our-rates for current rates.
