Boiler pressure drop

ThisIsWeird

Topped up five times - by how much (how far had it dropped each time) and what time spans?
And, importantly, if you top up the cold system to, say, 1bar, what then happens to the pressure over the first half hour after the CH is turned on?
Model of boiler, and type?
You can confirm whether water is coming out the discharge pipe outside by rubber-banding a wee clear bag over the end - always worth doing so that exit can be eliminated.

sevenhills

ThisIsWeird said:

Topped up five times - by how much (how far had it dropped each time) and what time spans?
And, importantly, if you top up the cold system to, say, 1bar, what then happens to the pressure over the first half hour after the CH is turned on?
Model of boiler, and type?
You can confirm whether water is coming out the discharge pipe outside by rubber-banding a wee clear bag over the end - always worth doing so that exit can be eliminated.

It's an Ideal boiler, I don't know the model, but it's around 6 years old.

The boiler man used a pump on one occasion, it drops down to zero within, maybe two weeks. I will be checking it today, if I am passing.

No leaking water is seen anywhere. When I topped it up to around 2 bar, it seemed to increase to 2 3/4 after 30 minutes, I thought that might be normal.

ThisIsWeird

sevenhills said:

It's an Ideal boiler, I don't know the model, but it's around 6 years old.

The boiler man used a pump on one occasion, it drops down to zero within, maybe two weeks. I will be checking it today, if I am passing.

No leaking water is seen anywhere. When I topped it up to around 2 bar, it seemed to increase to 2 3/4 after 30 minutes, I thought that might be normal.

The 'pump' the boiler man used was presumably an air pump, like for a bike or car tyre? And he sued this to pump up the Expansion Vessel, I'm guessing?

The EV is used to take in system water that expands when the boiler heats up, and release it when it cools down, so hopefully keeps the pressure reasonably steady.

2 bar is too high for a cold top-up. Yes, it's common for the pressure to increase when the system heats up, but it shouldn't be excessive, and 2.75bar is getting close to the 3bar 'safety' limit, where a release valve will blow open and dumps excess water outside via that copper pipe mentioned before.

Although it's tempting to do so 'cos there's a leak, you shouldn't really top up the pressure to more than say, 1.5bar, when cold; 1 bar is ideal for a working system.

It's helpful to know how quickly the pressure drops, as that will indicate how 'obvious' the leak should be. Very roughly, around, say, a cupful of system water will be lost to allow the pressure to drop from ~1 bar to 0.5bar (when many boilers will shut down). If you have that pressure drop occurring in a day, then, it should be very obvious indeed if it takes place in a visible area, like a rad valve. The same drop over a couple of weeks may well be evaporated away, and not be obvious - tho' you'd expect to see some scale and debris left behind.

The leak could also be occurring from inside the boiler, and this usually escapes either via the copper discharge pipe, of the plastic condensate one. Both should be monitored.