Intergas HRE Compact 36/30 pressure too high.

[snes]

First a brief history. Central heating was turned off over summer due to some rads being removed for decorating. After a few weeks, it was remembered to set parameter to HW only (doh!)

When rads eventually reconnected, parameter reset to CH+HW and CH fired up. Except it didn't!. Due to inactivity (?) pump had seized. Luckily it was one of the earlier ones - boiler is 12 years old - with the bleed screw. So it was possible to insert a long screwdriver and free off the pump.

Boiler now fired and seemed to operate well. Except a drip was observed coming from the prv pipe and a high bar reading was noted on the boiler - about 2.8 bar. With a spectacular lack of logic, I fitted a replacement prv. No improvement. Then I did what I should have done first - check the expansion vessel!

Sure enough, water came out of the Schrader valve indicating a failed diaphragm.

The EV was disconnected at the drain valve point and its rather black and brown contents dumped into a handy bucket. The EV was then completely isolated from the boiler and would now remain so as the option of fitting an external EV made practical and economic sense.

A new Intergas drain valve/EV point was installed although it probably wasn't necessary, a 12L Flomasta EV was connected to the original valve position using a genuine Intergas coupling. Just for good measure, yet another new prv was fitted.

History over! The problem is, with the EV precharged to 0.9 bar and the water side filled to the same, the CH will still fire up and operate as before, with no error codes, yet the boiler pressure still climbs to 2.8 bar in operation, falling slowly to 2.5 bar when cool. And, naturally, the prv still drips!

I have called Intergas technical support and explained the above and the only suggestion they could make is a faulty EV. Yet, I have taken the pressure at the Schrader valve and it is the same as the system pressure, which suggests that there is no blockage to it.

Can anyone suggest any further tests/actions I could take to isolate the problem, or even suggest what the problem is. Everything that could be a problem is brand new - prv, drain valve, EV and coupling. Sorry for the long post - thanks for making it this far!