BoilerFaultCodesWhat pressure should my boiler be?
Cold, with the heating off: 1 to 1.5 bar. That covers almost every domestic boiler sold in the UK. Running and hot, expect it to sit higher, and that is fine.
The figure that matters. Judge your boiler on this one.
Water expands. A rise of half a bar or so is normal.
What the manufacturers actually say
These are quoted from the manuals rather than rounded off, because the exact figure varies a little by make and your own manual is the final word.
| Manual | Instruction |
|---|---|
| Worcester Greenstar | "Fill the system to a pressure up to 1.5 bar" |
| Ideal Logic Heat | "Check system water pressure is between 1 & 1.5bar on the system pressure gauge" |
| Ideal Vogue Max | "With boiler off & system cold fill System to 1.0 Bar" |
| Ideal Logic Combi | "Will not operate if the pressure has reduced to less than 0.3 bar" |
Reading your gauge
| Cold reading | What to do |
|---|---|
| Under 0.5 bar | Too low. Top it up. Many boilers lock out down here. |
| 1 to 1.5 bar | Correct. Leave it alone. |
| 2 to 2.5 bar | High for a cold system. Bleed a little out. |
| Near 3 bar | The relief valve will discharge. Act now. |
Most gauges mark the normal band in green. If yours does, trust the green band over any general figure, including this page.
Fix whichever problem you have
Top up with the filling loop, step by step.
Bleed a little out and find out why it climbed.
Topping up weekly means a leak somewhere.
The relief valve has discharged. What next.
Why pressure matters at all
A sealed heating system is a closed loop of water under slight pressure. That pressure is what pushes water up to the radiators on the first floor and keeps air from being drawn in. Too little and the pump cannot circulate properly, so the boiler shuts down rather than run dry. Too much and the safety valve dumps water outside to protect the system.
A healthy system holds its pressure for months. Checking the gauge two or three times a year is enough, and early autumn is the sensible moment.
Safety
Topping up with the filling loop and bleeding a radiator are both fine to do yourself. Anything inside the boiler casing, on the expansion vessel or on the relief valve needs a Gas Safe registered engineer. If you smell gas, leave the house and ring 0800 111 999.
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
Affiliate links. We may earn a commission at no extra cost to you.