What pressure should my boiler be?
For most boilers, between 1 and 1.5 bar when the heating is cold. Some manufacturers allow up to 2 bar. It's normal for the reading to rise a little when the heating is on.
Check your reading
Choose your boiler brand, then move the slider to match your gauge. You'll see that manufacturer's recommended range and what they say to do.
Recommended pressure when cold for most boilers boilers: 1.0 to 1.5 bar.
Recommended cold pressure by brand
| Brand | Cold pressure | Source |
|---|---|---|
| Worcester Bosch | 1.0 – 1.5 bar | Worcester Bosch: boiler pressure FAQ |
| Ideal | 1.0 – 1.5 bar | Ideal Heating: Logic Combi troubleshooting guide |
| Glow-worm | 1.0 – 1.5 bar | Glow-worm: how to repressurise your boiler |
| Vaillant ecoTEC | 1.0 – 2.0 bar | Vaillant ecoTEC pro operating instructions (0020244996_01, 2017) |
| Baxi | 1.0 – 2.0 bar | Baxi: what should my boiler pressure be set at? |
| Vokera | 1.0 – 1.5 bar | Vokera Vision combi user, installation and servicing instructions |
| Viessmann | about 1 bar, top up to 1.5 bar | Viessmann: what to do if your boiler pressure is too low |
Pressure with the heating on
The reading rises as the water heats up. Vaillant says a gauge usually sits between 1 and 2 bar with the heating on. Baxi says the needle rises a little but shouldn't go higher than about 2.5 bar. Worcester Bosch says that if the pressure rises by more than 1 bar as the heating warms up, the expansion vessel may need repressurising by an engineer.
So always compare a cold reading with your manufacturer's range.
When boilers cut out on low pressure
Below a set point the boiler switches itself off and shows a fault code. The manufacturers' manuals give these figures:
| Boiler | Cuts out | Code shown | Source |
|---|---|---|---|
| Vaillant ecoTEC pro | below 0.5 bar | F.22 | Vaillant ecoTEC pro operating instructions (0020244996_01, 2017) |
| Vaillant ecoTEC exclusive | below 0.5 bar | F.22 | Vaillant ecoTEC exclusive installation and maintenance instructions (0020193968_05, 2021) |
| Vaillant ecoTEC sustain | below 0.3 bar | F22 | Vaillant ecoTEC sustain 24, 28, 34 installation and maintenance instructions (0020253094_06, 2021) |
| Baxi | below 0.5 bar | E118 | Baxi: boiler error codes |
| Vokera | 0.5 bar is the minimum for safe operation | A04 | Vokera Vision combi user, installation and servicing instructions |
If the pressure is too low
Your boiler will usually stop and show a fault code, such as Vaillant F.22, Ideal F1, Baxi E118, Glow-worm F.22 or Vokera A04. Topping up through the filling loop is a job your user manual covers:
- Let the heating cool down.
- Find the filling loop, usually under the boiler. Your manual shows where it is.
- Open it slowly and watch the gauge until it reaches the recommended cold pressure.
- Close the filling loop fully and reset the boiler if it's showing a fault.
If the pressure is too high
If you overfilled it, bleed a radiator until the gauge is back in range, as Worcester Bosch and Baxi both advise. Baxi says the reading shouldn't go above about 2.5 bar even with the heating on. If it stays high after bleeding, call an engineer.
If the pressure keeps dropping
Worcester Bosch says topping up once or twice a year is normal. More often than that means water is escaping somewhere. Find a Gas Safe engineer to trace it.
Fault codes linked to water pressure
Every pressure-related code on this site, by brand. Each page has that manufacturer's own steps.
Low pressure: topping up usually fixes it
Check the pressure first, then call an engineer if it's fine
Pressure sensor faults: engineer only
Common questions
What pressure should my boiler be?
Usually between 1 and 1.5 bar when the heating is cold, though some manufacturers allow up to 2 bar. Worcester Bosch, Ideal, Glow-worm and Vokera give 1 to 1.5 bar; Vaillant and Baxi give 1.0 to 2.0 bar. Your own manual has the exact figure.
How often should I need to top up boiler pressure?
Worcester Bosch says topping up once or twice a year is normal. If you're doing it much more often, water is escaping somewhere and you should contact an engineer or your installer.
How do I reduce boiler pressure if it's too high?
If it's high because the system was overfilled, Worcester Bosch and Baxi both advise bleeding a radiator until the gauge is back in range. If it stays high, call an engineer.
What should boiler pressure be when the heating is on?
A little higher than when it's cold. Vaillant says a gauge usually sits between 1 and 2 bar with the heating on, and Baxi says it shouldn't go above about 2.5 bar. Compare your manufacturer's range with a cold reading.
Is low boiler pressure dangerous?
No. A boiler with low pressure simply stops working and usually shows a fault code. Topping it up as your manual describes normally fixes it.
Sources
- Worcester Bosch: boiler pressure FAQ
- Worcester Bosch Greenstar 8000+ user instructions
- Vaillant ecoTEC pro operating instructions (0020244996_01, 2017)
- Vaillant: what pressure should my boiler be?
- Vaillant ecoTEC exclusive installation and maintenance instructions (0020193968_05, 2021)
- Vaillant ecoTEC sustain 24, 28, 34 installation and maintenance instructions (0020253094_06, 2021)
- Ideal Heating: Logic Combi troubleshooting guide
- Ideal Heating: boiler pressure too high, how to fix it
- Baxi: what should my boiler pressure be set at?
- Baxi: how to fix high boiler pressure
- Baxi: boiler error codes
- Glow-worm: how to repressurise your boiler
- Viessmann: what to do if your boiler pressure is too low
- Viessmann: what to do if your boiler pressure is too high
- Vokera Vision combi user, installation and servicing instructions
Last reviewed October 2026. Spotted something that doesn't match your manual? Email hello@boilercodes.co.uk and we'll check it. How we check