NK Gas Services
By NK Gas Services ▪ Gas Safe #568305 ▪ 5 min read
Quick answer: Low boiler pressure is usually caused by a small water leak, a recently bled radiator, or a faulty pressure relief valve. You can often re-pressurise it yourself — but if it keeps dropping, call a Gas Safe engineer.
Most boilers should operate at between 1 and 1.5 bar when the system is cold. You can check the pressure gauge on the front of your boiler — it's usually a dial or a digital display. If it reads below 1 bar, your boiler is low on pressure and may lock out or stop heating your home.
The most common cause. Even a tiny drip from a radiator valve, pipe joint, or the boiler itself will slowly drop the system pressure. Check around radiators, under the boiler, and along visible pipework for damp patches or corrosion.
Bleeding a radiator releases trapped air — but it also releases a small amount of water, which lowers the system pressure. This is completely normal. Simply re-pressurise the boiler after bleeding radiators.
The pressure relief valve (PRV) is a safety device that releases water if pressure gets too high. If it's faulty or worn, it can drip constantly and slowly drain the system. You may notice a small pipe outside your property dripping water.
The expansion vessel absorbs changes in water pressure as your heating heats and cools. If it fails, the PRV has to do all the work and keeps releasing pressure. This needs a Gas Safe engineer to diagnose and fix.
If your boiler pressure has dropped after bleeding radiators or naturally over time, you can top it up yourself using the filling loop. Here's how:
If your boiler pressure keeps dropping within a few days of topping it up, there is a leak or a fault in the system. Do not keep re-pressurising — this is a sign of an underlying problem that needs a Gas Safe engineer to diagnose properly.
If your boiler keeps losing pressure, NK Gas Services can diagnose and fix the problem same-day across Wolverhampton, Walsall, Cannock and the wider West Midlands. We charge just £50 for a diagnosis, which is deducted from your repair bill if you proceed.
Call your local Gas Safe engineers for a same-day diagnosis
Call 07404 922458£50 diagnosis ▪ Repairs from £75 ▪ No hidden fees