Ariston combi boiler losing pressure

[mastermiaow]

I have done quite a lot of reading on the web about this common problem.
At the moment the pressure drops to 0 when cold and remains at 0.5 when boiler is on. Recently the boiler got serviced and the guy pointed out the pressure was too low and increase the pressure by turning the tap under the boiler. The heating was noticeably hotter after that. I am not sure how long the pressure takes to drop but certainly within 24 hours. I understand the problem could either be in the pipes, radiator or boiler.

I have currently got the boiler off and increased water pressure to 2.5 to see if the problem is in the pipes/radiator. There has been no pressure drop in 5.5 hours. I have tied tissue around vertical pipes leading into and out of radiators and nothing is wet. I have never noticed any damp smell in the flat or water leakage up till now. So if nothing changes in next 6.5 hours, can I assume the problem is in the boiler?

Is there anything else I should be doing before calling a plumber? Would a boiler service necessary spot leaks or problems causing the pressure to drop? I have heard of products such as sentinel and x400 which clean gunge from system and seal leaks. I assume they are only worth a try if there is a pressure drop when the boiler isn't one - ie that the problem is in the pipes or radiator? Also I understand that they can harm some boilers - is this true?

Anyway thanks for your help, I'll have a go but hopefully I'll know when to call in the cavalry

 

[MANDATE]

Don't put the heating on while the pressure is at 2.5bar.
Your problem most likely started with the expansion vessel losing some of it' air charge, this would allow the water pressure to rise and open the Pressure relief valve at 3bar.
Unfortunately the PRV may not have closed properly due to sediment between valve seat and washer.
Best action is to set water pressure to 1bar, then put heating on and watch the pressure gauge rise. If it approaches 3bar, it will be a clear indication of the expansion vessel having lost some of the air.
If you imagine the vessel to contain a rubber balloon which is fully inflated then the water will squash the balloon when it expands and it makes the pressure rise by about 1bar.
But if the balloon is only partially inflated, it sends the pressure far too high and activates the PRV.
Even when the expansion vessel has been rectified the PRV if faulty will allow the pressure to drop without the heating being on.
I would suggest 9 out of 10 problems of this nature are related to expansion vessel and PRV. If not there is a leak elsewhere in the system

 

[mastermiaow]

Thanks for getting back.

Firstly how do I reduce the water pressure back to 1 bar???? I assumed I could do this by letting the boiler run and it would naturally lose pressure as in the past...
When the boiler was serviced the engineer set the pressure to about 1bar and when the boiler came on it increased to about 2. I don't think it ever went to 3. However this lasted a few hours. Next time the central heating went on, pressure was at back at 0.5. I assume that something is happening when the boiler goes that means it loses pressure...I am not sure therefore if the problem is 'balloon' is not inflating enough or too much

Thanks again

Matthew

 

[MANDATE]

To reduce pressure you could open the PRV, but I would suggest bleeding a radiator which makes sure the PRV stays intact.

You can check the balloon air pressure with tyre pressure gauge, that is when its cold and with zero water pressure. There are however some pitfalls.
There are two conditions to be met. (a) air pressure needs to be 0.8bar and (b) balloon needs to be max size so its essential the water side is open to atmosphere so any excess water can be discharged.

It's essential the vessel has max air capacity before expansion begins.

If the pressure is rising from 1bar to 2bar (approx) then that would suggest the vessel is ok, but the PRV could still be the cause of a small leak, if has been previously opened.

 

[mastermiaow]

Hi
Bled a radiator which did the trick. Have found wet tissue in one of radiator pipes in the bathroom which would explain why I didn't notice a damp smell. Looks like the nut between the radiator adjustor nob and the radiator is faulty so will have to investigate whether it's a job I can do. Assume will have to drain the whole system and take the radiator out?

Thanks again for your help

Matthew