Boiler Pressure Keeps Dropping? Here's What's Actually Causing It
If you keep topping up your boiler every week, the cause is usually one of three things. Here's how to tell which.
Topping up your boiler pressure now and then is normal. Doing it every week is not — it means water is escaping somewhere.
The three most common causes:
1. A small leak on the system. Check radiator valves, towel rail joints and visible pipework under floorboards. A pinhole leak under a board can drop pressure by 0.2 bar a week without showing a single drip downstairs.
2. A failed expansion vessel. The vessel inside your boiler absorbs the expansion of heated water. When it fails, the pressure relief valve dumps water outside through a copper pipe on the wall — check that outlet on a cold day, you'll often see drips or limescale staining.
3. A leaking pressure relief valve (PRV). Same outlet, different cause. The valve itself has failed and is dumping water continuously. Cheap fix — usually £80–£120.
What to do: check the external PRV outlet first. If it's dripping, that's your answer. If not, walk every radiator and pipework run with a torch and a kitchen roll square — a dry square stays dry, a damp one finds the leak.
Still can't find it? We trace hidden leaks with thermal imaging across Essex — same-week appointments, insurance-ready reports.
