vailliant ecotec pro 28 presssure problem

[diycooper]

In one of my properties just bought I have topped up the the central heating combi system. I turn heating on and boiler kick in alsoi I have hot water. After 30 mins the system goes from 1.5 bar to 0.5 bar and heating goes off. I have filled system many time and there is not sigh of water. There is also no sign of water by the boiler or coming out the pressure relief valve out side. What could this be ?

 

[MANDATE]

First thing to do is set pressure at 1.5bar, then put heating on and watch pressure gauge rise as it's supposed to do. Now does it stop about 2.5 bar or does it continue to 3bar.
The PRV is set to open at 3bar so if it goes to 3bar the problem is the expansion vessel.
You can secure a plastic bag on the end of the discharge pipe and see what it collects. Could be the small amount of discharge of hot water has dried when you examine it, making you think the problem is elsewhere.

Also could be leaking at PRV without heating on, which would be due to sediment between valve seat and rubber washer.

If the problem is not related to expansion vessel or PRV then you still have leak elsewhere

 

[diycooper]

had this looked at today by engineer and it was gthe expansion vessel. Alls it needed was air pumped into it. Shocking