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BOILER PRESSURE FAULTS

Boiler Relief Pipe Dripping

A dripping copper relief pipe usually means the pressure relief valve has opened because system pressure became too high or the valve is no longer sealing properly.

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Do not keep topping up a boiler that repeatedly loses pressure

Frequent pressure loss or excessive pressure indicates an unresolved fault. Stop if water is leaking, the relief pipe runs continuously or the boiler enters the red zone.

MOST LIKELY CAUSES

Start with these

Pressure too high The PRV may have opened to protect the boiler.
Expansion vessel fault Pressure can spike when heating runs.
PRV seat damaged Debris or wear may prevent resealing.
Filling loop passing Mains water may slowly increase system pressure.
◫ Symptom variations Match the exact pressure pattern and timing. ⌄
  • Copper pipe outside drips
  • White or green staining below outlet
  • Boiler pressure falls afterwards
  • Drip starts when heating runs
  • Pressure repeatedly climbs
✓ Quick checks Simple checks before arranging repair. ⌄
  1. Record the pressure when cold.
  2. Record it again when fully hot.
  3. Check visible radiator valves and pipework for leaks.
  4. Inspect the external relief pipe.
  5. Do not repeatedly repressurise.
1 Step 1 — Confirm the pipe source Allow the boiler and heating system to cool before checks. ⌄

Make sure the dripping pipe is the boiler relief discharge and not condensate.

2 Step 2 — Check system pressure Allow the boiler and heating system to cool before checks. ⌄

Compare the gauge when cold and hot.

3 Step 3 — Do not cap or block the pipe Allow the boiler and heating system to cool before checks. ⌄

The discharge route is a safety feature and must remain open.

⌁ Common causes explained Why boiler pressure faults develop. ⌄

A dripping copper relief pipe usually means the pressure relief valve has opened because system pressure became too high or the valve is no longer sealing properly.

⌘ Advanced diagnostics Heating-engineer checks and repair work. ⌄
  • Test PRV operation and reseating.
  • Check expansion vessel pre-charge.
  • Inspect filling loop for passing.
  • Check pressure sensor.
  • Verify safe discharge termination.
▣ Parts that may need replacing Common components linked to this fault. ⌄
  • Pressure relief valve
  • Expansion vessel
  • Filling loop
  • Discharge pipe
  • Pressure sensor
! When to call a heating engineer Conditions that should end basic troubleshooting. ⌄
  • Pressure drops repeatedly.
  • Pressure enters the red zone.
  • The relief pipe drips continuously.
  • A leak is hidden or internal.
  • The expansion vessel or PRV may be faulty.
? Frequently asked questions Common boiler pressure questions. ⌄

What pressure should a boiler show?

Many sealed systems sit around 1 to 1.5 bar when cold, but always follow the boiler manual.

Is frequent repressurising normal?

No. It indicates ongoing water loss or a pressure-control fault.