Central heating leak detection in London finds the pinhole on a sealed system that keeps losing pressure, without breaking through every wall and floor to look.
Pressure loss on a sealed system is the symptom we are asked about most often. The boiler drops from 1.2 bar to 0.8 bar over a few days, and the customer tops it up at the filling loop. Within a week the gauge has dropped again.
Unlike a mains-fed plumbing leak, the system is closed, inhibitor-dosed (Sentinel X100 or Fernox F1) and circulates only between the boiler, the pump, and the radiators. A small loss can hide for months without showing as a wet patch. The leak rate is too low to soak through a ceiling, but fast enough to push the system below the low-pressure cut-out. This survey finds where it is going before you redecorate over the wrong wall.
We charge to working pressure with a mains-fed filling loop. Then we isolate the boiler from the loop at the flow and return service valves. That lets us pressure-drop test the radiator circuit separately from the boiler internals (heat-exchanger pinhole, diverter-valve cartridge seal, expansion-vessel diaphragm rupture).
Once the loss is narrowed to either side, we move zone by zone until the leak rate localises. We isolate ground floor from first floor, and microbore runs from 22mm trunk runs.
Thermal imaging with a FLIR camera on hot pipework finds cold trails of leaks under floors. Tracer gas (the standard 5 per cent hydrogen and 95 per cent nitrogen mix) is introduced into the depressurised circuit and read at the surface with a Sewerin Variotec. This pins the pinhole to within centimetres.
Common London-stock sources:
- corrosion pinholes on radiator return tappings (the cold-leg oxygen side)
- perished pump-head seals on older Grundfos UPS units
- towel-rail valve tail glands
- pinholes on 8mm microbore under suspended timber floors
After any top-up we redose inhibitor to BS 7593.
Where this service applies
- Boiler pressure dropping from 1.2 bar to under 1.0 bar within days of topping up
- Filling loop being used weekly or more often to keep the system in range
- Damp patch under a radiator, on a towel-rail valve tail, or beneath a heating-run board
- Recurring low-pressure boiler lockouts after the system has run hot
- Microbore under suspended timber floors in Victorian and 1930s London terraces
- Heating-side leaks behind plastered walls with no visible trail
- Pre-power-flush check to rule out a leak before chemicals are introduced
- Insurance trace-and-access on a heating leak with insurer-grade report
How we deliver
No surprises, no upselling. The exact path every job follows.
- 1
System recharge to working pressure
Filling loop opened, system brought to 1.2 bar cold. Gauge sealed and watched. - 2
Boiler isolation and split test
Flow and return service valves closed so the loop and the boiler internals are pressure-tested separately. Drop rate measured on each side over 30 minutes. - 3
Boiler internal check
If the boiler side drops we check the expansion-vessel pre-charge, diverter-valve cartridge seal, heat exchanger for pinholes, and pump-head gasket. - 4
Zone isolation on the loop
Loop-side drop, we isolate ground floor from first floor, microbore from trunk, towel-rail circuits from radiator circuits, until the leak localises to a specific zone. - 5
Thermal imaging sweep
FLIR camera over the suspect zone with the system hot, looking for cold trails on floor and wall finishes where heated water has been escaping. - 6
Tracer gas localisation
5 per cent hydrogen and 95 per cent nitrogen mix introduced into the depressurised zone, surface scan with a Sewerin Variotec to pin the leak point to within centimetres. - 7
Repair quote and inhibitor redose
Written report with leak location, photographs, and a separate repair quote. After any top-up we redose Sentinel X100 or Fernox F1 to BS 7593.