Unvented system pressure rising

[csk423mfb]

Just joined and looking for advice if possible.

I have an unvented heating system which consists of a worcester bosch greenstar gas boiler, hot water cylinder controlled by 2no. 2 port valves, 1 for the heating and 1 for the hot water circuit to the cylinder.

The pressure usually sits around 1-1.5 bar, I noticed the other night it had risin to 3bar and activated the sfatey valev on the boiler and dumped some water. I took the pressure out by opening the PRV on the heating circuit and it dropped down but quickly rose again to over 3 bar (30mins ?)

I decided to check the quick fill loop and found the ball valve passing so swapped this out. Still pressure was rising. I checked the exp vessel (separate vessel not part of the boiler) the air valve was leaking ever so slightly so I swapped this out. Still rising.

I then noticed that the hot water had a slight colour / smell to it. I decided to isolate the Heating circuit (closed the 2 port valve and closed the LSV) to the cylinder as I suspected the coil has burst in the cylinder leaking the heating circuit into the hot water supply. Im currently using the electric immersor for hot water. This has cleaned the hot water up but my heating circuit is still rising up to 3 bar.

Can anyone shed light on if my assumption above regards the coil is correct and why the pressure is STILL rising ???

cheers

 

[simond]

Assume you have an unvented cylinder?

In which case, and assuming also that LSV is lockshield valve, I would suggest disconnecting the coil connections (bearing in mind the jeopardy factor if the coil is holed) and seeing if it is leaking*. Chances are either the motorised valve or the LSV is letting through the pressure, which means you need to have a builders bag handy.

*NB: I assume when you say the air valve was leaking on the ex vessel you swapped the whole vessel out not the valve? Otherwise you are are wasting your time. Change the EV before doing anything else.

 

[csk423mfb]

Assume you have an unvented cylinder?

In which case, and assuming also that LSV is lockshield valve, I would suggest disconnecting the coil connections (bearing in mind the jeopardy factor if the coil is holed) and seeing if it is leaking*. Chances are either the motorised valve or the LSV is letting through the pressure, which means you need to have a builders bag handy.

*NB: I assume when you say the air valve was leaking on the ex vessel you swapped the whole vessel out not the valve? Otherwise you are are wasting your time. Change the EV before doing anything else.

Yes the whole vessel was swapped out for a new one and the hot water cylinder is also unvented.

Your thoughts might be right regards the LSV/Motorised valve still letting the pressure through. When I run the hot water ie bathtime and discharge a fair amount the pressure drops on the heating system gauge.

I'm planning on calling a plumbing pal to look at it further but wanted to get some advice on where I'd got to so far I'll leave the coil disconnection to him. Thanks for the response, looks like a new cylinder is needed ! even when it's only 18 years old.