The gauge on the front of a combi boiler should sit between 1 and 1.5 bar when the system is cold, rising a little as it heats up. If you are topping it up more and more often, the rate is the diagnosis.
How often is too often?
| How often you top up | What it usually means |
|---|---|
| Once or twice a year | Normal. Systems lose a little over time, especially after bleeding |
| Every few weeks | Water is going somewhere: a leak on a radiator, a valve or the pipework |
| Every few days | Find it now. You are putting a lot of fresh water in |
| High when hot, low when cold | The expansion vessel has lost its air charge |
Write the date down every time you top up. Within a month you will know which line you are on, and it is the single most useful thing you can tell a heating engineer on the phone.
Where to look yourself
- Outside, near the boiler: a small copper pipe. If it is dripping or there is staining below it, the pressure relief valve is passing.
- Under each radiator and around the valves: look for staining, damp carpet or a white crust.
Why topping up is not the fix
Every top-up brings fresh, oxygen-rich water into the system. That speeds up the internal corrosion that makes sludge. A small leak left alone for a winter, topped up every week, is how a clean system becomes a sludged one.
Expansion vessel
If the pressure swings well over 2 bar when the heating runs and drops under 1 when it is cold, the vessel inside or beside the boiler has lost its charge. That is a recharge or a replacement. No amount of topping up will ever fix it.
What we do
We find which of the two it is, a leak or the vessel, before we quote. The repair is priced once the fault is known and before anything is done. Send us the job or ring 07712 646488.