Central Heating System loses pressure.

[ColinJames]

I have an Ariston Clas HE EVO System boiler. Over the last few months, getting on for a year, the sytem loses pressure. Not regularly or constantly. It was working ok for weeks, months and then when I get up in the morning pressure would be a zero. This is getting more frequent. I repressurize, check everyday and there would be no change then suddenly, zero. I never seem to catch it half way. The pressure regulator has 1.4 bar when the system is at zero and I tied a bag onto the relief valve discharge and it is empty. I can't see any leaks from the boiler. It takes minimum input to repressurize. It is an old house, radiator pipes are under the floors and hard to get to. I've had a quick look and can't see anything.
So question is how do I find the leak location? Although the boiler looks ok, the fact that the everying works, then suddenly the pressure drops and recharging is a minimum amount, makes me think it is something getting switch on/off and leaking at one position. The zone valves are under the boiler and easy to see and there are no leaks there. When the central heating was on, all radiators were hot right to the top, no air trapped. And if it is the radiator pipes, is there a quick way to identify where the leak is?

Any suggestions welcomed.

 

[denso13]

And if it is the radiator pipes, is there a quick way to identify where the leak is?

You could isolate sections of the pipework but that will involve capping/turning off different areas.

 

[ColinJames]

Thank you.
With the layout of the house, that would be a big job.

 

[Mister Banks]

Presumably in this weather you are only heating the HWC therefore the radiators are isolated at the motorised valve. This suggests that the "leak" is somewhere in the boiler or the hot water circuit.

 

[ColinJames]

Thank you Mister Banks. Yes, that's my logic...although my logic has failed me before.

 

[denso13]

Thank you Mister Banks. Yes, that's my logic...although my logic has failed me before.

They aren't completely separate, they'll both be connected to a common return so either could be leaking.

 

[CountryFan]

Could be the expansion vessel or automatic air vent if fitted.

 

[Johntheo5]

I have an Ariston Clas HE EVO System boiler. Over the last few months, getting on for a year, the sytem loses pressure. Not regularly or constantly. It was working ok for weeks, months and then when I get up in the morning pressure would be a zero. This is getting more frequent. I repressurize, check everyday and there would be no change then suddenly, zero. I never seem to catch it half way. The pressure regulator has 1.4 bar when the system is at zero and I tied a bag onto the relief valve discharge and it is empty. I can't see any leaks from the boiler. It takes minimum input to repressurize. It is an old house, radiator pipes are under the floors and hard to get to. I've had a quick look and can't see anything.
So question is how do I find the leak location? Although the boiler looks ok, the fact that the everying works, then suddenly the pressure drops and recharging is a minimum amount, makes me think it is something getting switch on/off and leaking at one position. The zone valves are under the boiler and easy to see and there are no leaks there. When the central heating was on, all radiators were hot right to the top, no air trapped. And if it is the radiator pipes, is there a quick way to identify where the leak is?

Any suggestions welcomed.

You say it takes minimum input to repressurize it.
If you have say a 10L EV (expansion vessel) that might normally be pre charged to 1.0bar and you then charge it to 1.4bar, then that will take 1.67L to do so which means that you are possibly losing/leaking 1.67L each time the boiler pressure falls to zero but you would normally take ~ maybe over a minute or so to do this except you fully open the filling valve. If the pre charge pressure is 1.4bar then it will only require a few ml of water, say 0.2L or less to recharge it so you may have no leak.
Assuming the boiler pressure is 1.4bar cold, what is it after doing a HW cylinder re heat?

Suggest checking /get checked the EV pre charge pressure as a start + the air vent as suggested above.

 

[ColinJames]

Thank you for these suggestions.
There are only two air vents fitted, on the boiler itself and an automatic on the heating loop at the HW cylinder. Boiler has clear water when cracked open. The heating loop air vent (small bucket type) is at the back of a cupboard and the area is dry. It is about 2-3 years old as previous leaked and made a mess of the area but as I say is dry when I checked. I think I'll put a bag around it and see it it collects anything over a few days.
It is not the original EV but this one has been in place for 5+ years and when checked on the depressurized system with independent gauge showed 1.4 bar. But, I think I will depressurize the lot and reset, if only for peace of mind.

 

[Johntheo5]

Well, if the depressurized and filling pressures are the same, in your case @ 1.4bar, then the tiniest drop of make up water will restore the boiler pressure. The main reason for having a difference of ~ 0.5bar between the precharge and filling pressures is to give a nice little water reserve which avoids frequent top ups.

A 8L EV with precharge/filling pressures of 1.0bar/1.4 bar gives a reserve of 1.33L, a 10L...1.67L & a 12L....2.0L.