Your boiler pressure is reading too high and you’re worried something’s going to fail or leak.
Is this your problem?
The pressure gauge is above 2.5–3 bar when the heating is on, or stays high even when cold.
What to do
- Turn the boiler off and let it cool fully (30–60 minutes).
- Check the gauge again when cold.
- If it’s still above 1.5 bar, pressure really is too high.
- Do not keep resetting or topping up. That makes it worse.
Safe DIY: Yes, checking only.
Stop and call a pro if pressure is above 3 bar or the relief pipe is dripping.
Is this your problem?
Pressure rises every time the heating comes on, then drops a bit when it cools.
What to do
This usually means the expansion vessel has failed or lost air.
- You can’t fix this properly without tools.
- Running it like this stresses pipes and seals.
- Switch heating off if pressure climbs near 3 bar.
Safe DIY: No.
Call a Gas Safe engineer – this is a common repair.
Is this your problem?
Pressure shot up after you topped up the boiler.
What to do
You’ve likely overfilled it.
- Find the radiator bleed key.
- Bleed one radiator slowly (start downstairs).
- Watch the gauge drop to 1–1.5 bar (cold).
- Close the valve tightly.
Safe DIY: Yes.
Stop if water won’t stop or pressure won’t fall.
Is this your problem?
Pressure keeps rising even though you haven’t topped it up.
What to do
The filling loop valve may be leaking.
- Look under the boiler for the silver braided hose.
- Make sure both valves are fully closed.
- If pressure still climbs, the valve is faulty.
Safe DIY: Checking and closing only.
Call a pro if it keeps rising.
Is this your problem?
Water is dripping from the copper pipe outside.
What to do
That’s the pressure relief valve doing its job.
- This means pressure is dangerously high.
- Don’t ignore it or cap the pipe.
- Turn heating off if possible.
Safe DIY: No.
Urgent Gas Safe call needed.
Is this your problem?
Pressure reads high but the heating feels normal.
What to do
The pressure gauge may be faulty.
- Compare with system behaviour (no leaks, no noise).
- Still needs confirmation by an engineer.
Safe DIY: No repair.
Call a pro at next service.
Quick safe pressure guide (UK combi boilers)
| Boiler state | Normal pressure |
|---|---|
| Cold (off) | 1.0–1.5 bar |
| Heating on | Up to ~2.0 bar |
| Overpressure risk | 2.5 bar+ |
| Dangerous | 3.0 bar |
When to stop DIY immediately
- Pressure hits 3 bar
- Water leaking outside
- Boiler locking out repeatedly
- You don’t know where the filling loop is
At that point, turn the heating off and call a Gas Safe registered engineer.
With the help of this guide, you will be successful in fixing your boiler pressure issue.
Is it safe to fix this yourself in the UK?
Partly, only basic pressure checks are DIY-safe.
You may bleed a radiator carefully or check the pressure gauge.
Do not open internal boiler parts or touch the PRV.
If pressure rises again after bleeding, stop and call a Gas Safe engineer.