Please help.
Can someone kindly explain what are the key indicators are that my combination boiler expansion vessel needs to be replaced?
If the vessel pressure is checked when the boiler is switched on and under pressure would it disperse water when a pump is attached and re-pressuring it with a bike pump?
What I have learned and understand so far is that there should be a release of air from the valve when activated when the boiler is switched on or off.
If the expansion vessel diaphragm is faulty when the air valve is engaged then water should/will come out?
However if the system is under pressure then my understanding is that of course water would come out of the air valve and the person doing the job is trying to con me into getting unnecessary work?
***Update***
Answers to your various comments - The boiler was checked with pressure in the boiler also when given the combustion receipt I compared with a previous receipt and quickly noticed that the device that has been used is out of date of its calibration so gave of incorrect readings. I showed the couple the door and did not pay. I believe that the boiler pressure continues to drop though very slowly and sometimes has gone into the anti frost 5°C area, there is pressure in the boiler though it isn't been driven over 3 bar 2.5bar max which I understand this is good?
It's just the drop in beyond normal pressure which I do not understand, will place a bag over the pipe to see if any water is trickling outside.
Many thanks in advance for your help.