What boiler pressure loss is ok over time?

ElizaC · May 8, 2022

My Ideal boiler pressure gauge pointer shows about 0.85 when cold (about 1.8 when the heating is on).
10 weeks ago the readings were 1.0 when cold and 2.0 when hot.
Clearly there is a loss in pressure over time. I can see no leak on any radiator or near the boiler. Is this pressure drop of about 0.1 bar a month normal or do I need an engineer to look at it. A new sump was fitted 10 weeks ago which is when I started watching the pressure.
Thank you for any advice.

John.g · May 8, 2022

You would really need to know the E.vessel capacity and the prefill (air end pressure) and filling pressure. If you assume a 8 litre EV with prefill/filling pressures of 0.75/1.0bar then the EV will have a reserve of 1.0 litres when cold (at 1.0 bar), it will then lose ~ 0.4 litres (0.37) in falling by 0.1bar, to 0.9bar cold so 0.1bar/month or 0.37 litres or 4.5 litres/annum, excessive IMO. On the other hand if the prefill/filling pressures are the same then the slightest leak will lead to this pressure drop.

If you are really concerned about the pressure drop then wait until the system is cool again, note (again) the pressure, repressurize to exactly 1.0bar, open any radiator air vent and measure the amount of water that vents while the pressure falls again to the original pressure. A bit of a pain but the only way in the absence of not knowing the original conditions/pressures.

Ben-gee · May 8, 2022

Is it still losing pressure?

You said the system was worked on and then it lost pressure, this could just be losing air through an automatic air vent and now the air has gone the system is stable?

ShaunCorbs · May 8, 2022

0.25 isn’t much I would monitor for the next 6 months if it looses around the same within then it’s fine

ElizaC · May 8, 2022

British gas did their annual service and found a cracked sump which they replaced. It stayed at about 1bar for a month and now 2.5 months later its just below 0.9. It is really hard to see exactly as you can't look straight at the gauge, only at an angle from below but it's definitely below 1. You also have to tap the gauge to read it as it seems to get stuck when the heating goes on. I don't want British gas to come out unless there's actually a problem, I know some pressure loss just happens over time. Sometimes they seem to cause problems that weren't there before! Just don't know what to do for the best as don't want kids to be left without hot water as I didn't fix the boiler. Thanks for the help x.