Boiler pressure drops every few days — finding the leak
A sealed system that needs topping up more than once or twice a year is losing water. Repeated refilling introduces fresh oxygen every time, which accelerates internal corrosion — so it's worth chasing even when the drop is small.
Where the water usually goes
Three places: out through the pressure relief discharge pipe, out of a joint or radiator valve, or nowhere visible because a failed expansion vessel is causing pressure swings that lift the PRV every heating cycle. We check the discharge pipe outside first because a wet or limescaled outlet answers the question immediately.
The diagnostic order
- External PRV discharge inspected for evidence of weeping
- Expansion vessel charge tested against system pressure, cold
- Visible joints, valves and radiator tails checked under pressure
- Buried pipework assessed where nothing else accounts for the loss
Frequently asked
- Is topping up harmful?
- Occasionally, no. Weekly, yes — each refill brings dissolved oxygen that corrodes steel radiators from the inside.
- Can a vessel be recharged rather than replaced?
- Often yes. If the diaphragm has failed it needs replacing, and we can usually fit an external vessel where the internal one is inaccessible.
- What about leaks under the floor?
- We use thermal imaging and pressure testing to narrow the location before anything is lifted.
Small leaks get expensive
The cost of finding a leak is almost always lower than the cost of the corrosion damage that follows two years of weekly topping up.
Related solutions
Core services
Where we cover
New Worcester boiler with a 10 year guarantee*
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