Boiler losing pressure fix across London

Pressure gauge sitting below 1 bar, or dropping every few days no matter how often you top it up? That is rarely a stable system, and topping up indefinitely will eventually destroy your boiler. We diagnose the loss, fix it at source, and repressurise correctly.

A healthy sealed system in a typical London property should sit between 1.0 and 1.5 bar cold, rising to roughly 1.8 to 2.2 bar at full temperature. When pressure falls below 1 bar the boiler locks out, displaying a low-pressure code such as Vaillant F22, Worcester 1170, Ideal F1, or Baxi E118. The instinct is to grab the filling loop, but each top-up dilutes your Sentinel X100 inhibitor, accelerates internal corrosion, and masks the real fault. Pressure loss almost always has a cause: a perished expansion vessel diaphragm, a passing pressure relief valve discharging through the external overflow, a hairline radiator pinhole, or a failing auto air vent on the boiler itself.

Our engineers attend with a calibrated test gauge, a Schrader pressure tester for the expansion vessel, and a thermal-imaging camera to trace damp patches in floors and walls. We carry common internal vessels for Worcester Greenstar, Vaillant ecoTEC, and Ideal Logic, external Zilmet and Flamco add-on vessels, replacement Caleffi PRVs, and fresh Sentinel X100 to dose the system after refill. Once the cause is fixed, we vent every radiator, rebalance, and repressurise to the manufacturer's cold-fill specification.

How we deliver

No surprises, no upselling. The exact path every job follows.

1. 1
   Gauge and history check
   We read both the on-boiler gauge and a calibrated test gauge, then ask how often you have been topping up and what the discharge pipe outside is doing.
2. 2
   Leak survey, visible and hidden
   Inspect every radiator valve, towel rail, airing-cupboard joint, and pump. Thermal-imaging camera used to find leaks below floors and behind walls.
3. 3
   Expansion vessel pre-charge test
   System depressurised, Schrader valve checked. Healthy domestic combi reads 0.75 to 1.0 bar on the air side. Re-charged or replaced as required.
4. 4
   PRV and auto air vent inspection
   Pressure-relief valve checked for passing. Auto air vent on the boiler header re-seated or replaced if it has stuck open.
5. 5
   Repair quoted and carried out
   Written quote presented before any chargeable parts work. Repair completed using OEM or equivalent parts.
6. 6
   Controlled refill and inhibitor dose
   Filling loop opened slowly to avoid air-locking the pump. Fresh Sentinel X100 dosed in line with BS 7593 to restore corrosion protection.
7. 7
   Bleed, balance, and reset to cold-fill spec
   Every radiator and towel rail vented, lockshield valves balanced, and final cold pressure set to manufacturer specification.
8. 8
   FGA and sign-off
   Flue-gas analyser run to confirm safe combustion after the system is back up to temperature, then written hand-over with pressure readings.