Your boiler's pressure gauge keeps creeping down into the red, the heating cuts out, you top it back up — and a few days later you're doing it all again. It's one of the most common things Derby homeowners call us about as the heating season gets going, and it's worth understanding, because the difference between a harmless one-off and a sign of a leak is important. With energy now costing more after October's price-cap rise to around £1,723 a year, you also don't want a boiler running inefficiently all winter.
What boiler pressure should be
Most combi boilers run best with the pressure gauge sitting between about 1 and 1.5 bar when the heating is off (always check your own boiler's manual, as models vary). If it drops below 1 bar, the boiler often shuts down as a safety measure and won't fire until it's topped back up. A gradual, very slow drop over many months can be normal. A noticeable drop every few days is not — that water is going somewhere.
How to top it up safely
Topping up is something many households can do, using the filling loop — the silver braided hose beneath the boiler. Check your manual first, then:
- Turn the boiler off and let it cool
- Open both valves on the filling loop slowly — you'll hear water flowing in and see the gauge rise
- Close the valves as the needle reaches the level your manual specifies (usually around 1.2–1.5 bar) — don't overfill
- Switch the boiler back on; it should now fire normally
- If you can't find the filling loop or aren't confident, stop — this is a fair point to call an engineer rather than guess
When repeated pressure loss means a leak
A sealed heating system shouldn't lose water. If you're topping up regularly, the water is escaping somewhere — and finding where is a job worth doing before it causes damage.
Treat it as more than a top-up, and call us, if:
- You're refilling every few days or more often
- You can see damp patches, staining or drips around radiators, valves, pipework or under the boiler
- There are watermarks on ceilings or walls near pipe runs
- The pressure also spikes very high when the heating is on — which can point to a failed expansion vessel rather than a leak
- You've topped up but the boiler still won't hold pressure or keeps locking out
"One top-up a year is normal housekeeping. One top-up a week is the system telling you water is getting out somewhere — and that's worth finding early."
Why catching it early matters
A small internal leak rarely stays small. Left alone it can damage flooring, ceilings and the boiler itself, and escaping water is now behind a large share of UK home insurance claims. Catching a persistent pressure drop early is far cheaper than dealing with the water damage later. If you're topping up more than occasionally, have it looked at. Call Out Repair covers Derby and Derbyshire 24/7 — we can trace where the pressure is going and put it right.
Topping up too often? Let's find the cause
If your boiler keeps losing pressure, our Derby and Derbyshire engineers can trace the leak and fix it — day or night.
Published by Kirk Group Editorial
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