I have a Boiler Combi 24 (UK) and this morning I just noticed that the pressure indicator is pointing to 0. However everything is working fine, I have heating and hot water.

Usually when the pressure is at 0 the boiler indicates (Failure) and there is no heating / hot water..

  • I have tried to reset the Boiler but no luck
  • I have tried draining the boiler, once all the water got out the Boiler indicates Failure, which is fine, and then I have open the looping thing to make the pressure go up. It did go up because the boiler started working again but the pressure indicator is still stuck at 0.

Can someone explain me why the indicator is always at 0 ? Is it broken ? Is there something stuck in the pipes ?

(Note that 5 days ago I had a new shower installed in my bathroom and some plumbing work was done in there, not sure if that can help debugging the situation)

Here's the bottom of the boiler, with the meter:

Bottom of combi boiler

Here's a closeup of the meter:

Possibly broken pressure indicator

  • Hello, and welcome to Stack Exchange. Is this a mechanical pressure meter? Where on the piping is it located? (A picture could help.) Mar 31, 2018 at 11:57
  • @DanielGriscom I have added a pics in the main thread. It's a mechanical gauge.
    – Paulus2
    Mar 31, 2018 at 12:06
  • 2
    You've encountered the most common variety of pressure gauge: broken.
    – hobbs
    Mar 31, 2018 at 12:46
  • that is not zero .... it is pegged at maximum
    – jsotola
    Mar 31, 2018 at 21:23

2 Answers 2


Take a close look at the needle of the meter:

Closeup of possibly broken meter

There's a pin at about 7 o'clock on the dial that the needle would rest against if it were reading zero. But, the needle isn't against that pin; it either jumped the pin and is reading about negative 0.5 bar (pretty unlikely), or it's actually beyond the top of the range and reading about 4.8 bar (more likely).

Looking at the manual for your heater, and at the diagram for the connections at the bottom of your heater, that meter is on the heating circuit. The manual gives a maximum operating pressure of 2.5 bar (the safety valve is set to go at 3 bar). If the meter is accurate, then the safety valve has failed and your heating circuit is running at dangerous pressures. It's actually more likely that the meter is broken, and the needle is just hanging straight down due to gravity. Hard to tell without more information.

  • It's improbable: all boiler have safety pressure-release valves that releases water if pressure goes over 3 bar. If there's no leakage it simply a broken manometer. PS: try to open the valve behind the manometer itself (it should be there to enable pressure read-out).
    – DDS
    Mar 31, 2018 at 14:11
  • @DDS Something has failed, and it isn't clear what, but you're right: the meter is more likely to fail than the safety valve (which probably has to meet strict reliability requirements). Edited to clarify: thanks. Mar 31, 2018 at 14:45

Almost surely what is broken is the manometer itself.

Assuming that boiler has low-pressure pressostat.

If radiators work -> there is sufficient pressure in primary loop
If DHW works (assuming is instantaneous) -> there is sufficient pressure in primary loop (DHW exchanger is connected by 3-way to primary loop)

If the boiler doesn't do 'pounding' noise (air bubbles due to low pressure) or boiler doesn't gives an error it mean that pressure is enough high not to cause issues.

The only thing that can be broken is the manometer itself.

Try with a rubber hammer try to gracefully hit the manometer (caring not to hit the glass) to see if gets unstuck.

I wouldn't even fix it if boiler gives a specific error: I can restore the pressure 'little by little' and, as soon as the error goes away I'll give little more pressure (1 second of feed open). Boiler can safely work between 500 and 3000 hPa, so there's enough margin to operate it.

You can ask your plumber to fix it at yearly boiler maintenance, there's absolutely no urgency.

EDIT: Try to: close home water supply then purge at least 3L from a radiator purge valve and see if pressure goes down. If it does your boiler has a faulty pressure release valve (has to be fixed as soon as possible), if gauge doesn't move it's a stuck manometer

It also looks like all valves (flow, return and fresh-water) are closed -> is your system running?


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