If your boiler is losing pressure, it usually means water is escaping somewhere or the system hasn’t been topped up properly. The good news is that in many cases you can fix it yourself.
First: check the pressure gauge
- Most boilers should sit around 1.0–1.5 bar when cold.
- If it’s below 1 bar, you’ll need to repressurise.
How to top up (repressurise) your boiler
- Turn the boiler off and let it cool.
- Locate the filling loop (a flexible silver hose under the boiler, or built-in taps on newer models).
- Slowly open the valves—listen for water flowing.
- Watch the pressure gauge and stop when it reaches about 1.2–1.5 bar.
- Close the valves tightly and turn the boiler back on.
If pressure keeps dropping
That’s when you need to look deeper:
1. Check for leaks
- Look around radiators, valves, and pipework for drips or damp spots.
- Even a tiny leak can cause pressure loss over time.
2. Recently bled radiators?
- Bleeding releases air but also lowers pressure.
- Just repressurise again afterward.
3. Faulty pressure relief valve (PRV)
- If water is dripping outside from a pipe, the PRV might be letting water out.
4. Expansion vessel issue
- This helps regulate pressure. If it fails, pressure may drop (or spike when heating is on).
When not to DIY
Call a Gas Safe engineer if:
- You’re topping up frequently (e.g., every few days)
- You see water coming from an outside pipe
- Pressure drops to zero repeatedly
- You suspect an internal boiler fault
Quick rule of thumb
- One-off drop? Top it up.
- Keeps happening? There’s a fault that needs fixing.