Combi Boiler Pressure Loss in Woking
A homeowner in Woking reported that their combi boiler was losing pressure daily — they had to repressurise it every morning using the filling loop. The boiler would drop from 1.5 ...
Response time
2 hours
Time on site
3 hours
Cost range
£210
Warranty
12 months
The Problem
A homeowner in Woking reported that their combi boiler was losing pressure daily — they had to repressurise it every morning using the filling loop. The boiler would drop from 1.5 bar to 0.3 bar overnight and sometimes shut down with a low-pressure fault code.
There were no visible leaks on any radiator, valve, or pipework in the property. The boiler was a Worcester Bosch combi, approximately 7 years old.
The Diagnosis
We pressure-tested the system and confirmed it was losing pressure steadily. We checked all visible pipework, radiator valves, and the boiler's internal pressure relief valve discharge pipe — all dry. The pressure relief valve (PRV) was tested by checking the discharge pipe outside — no water was present, ruling out a PRV fault.
We suspected a hidden leak on the heating pipework. Using acoustic detection, we traced the sound of escaping water to beneath the ground floor. The property had suspended timber floors with pipework running beneath. We lifted a floorboard in the corner of the living room and found a pinhole leak on a 15mm flow pipe where it had been resting on a brick sleeper wall, gradually wearing through.
The Repair
We isolated the boiler and drained the heating system down. We cut out the damaged section of pipe — approximately 4 inches with the pinhole — and replaced it with new 15mm copper joined with compression fittings. The pipe was re-routed slightly and sleeved where it passed over the brickwork to prevent future abrasion.
The system was refilled, vented, and repressurised. We added a system leak sealer as a precaution against any other minor weeps in the under-floor pipework. The boiler was fired and the pressure was monitored — stable at 1.5 bar with no drop over the following hour.
Acoustic detection traced leak under ground floor
Lifted floorboard and repaired pinhole in flow pipe
Refilled, added leak sealer and monitored pressure
Outcome & Advice to the Homeowner
The pressure loss was resolved — the boiler held steady at 1.5 bar overnight for the first time in weeks. The homeowner was relieved that the hidden leak had been found and repaired without needing to lift the entire floor.
We recommended monitoring the pressure over the following week and advised that if the pressure dropped again, there may be additional minor leaks in the under-floor pipework that would require further investigation.
Job Summary
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