Alpha CB28X loosing pressure after CH program.

[JimmyBurnWorld]

Hi DIYnotters,

First post so be kind!

I have an Alpha C27 EDIT:CB28X combi which keeps loosing pressure. If I fill it to the cold green 'normal' pressure, it will run for days on end, but once the CH demand turns off, the pressure drops almost to zero. This hasn't been too bad over the festive period as we've just had the CH on constantly, but now we're back to programmed CH it's going to be a pain in the proverbial! (I write this from a very cold front room)

This morning I woke early to a cold house, filled the boiler, took a leak, checked the boiler, back to zero bar!

Filled it again and turned the CH on straight away, and it's been running for an hour. Turned the CH off and within a couple of minutes zero bar.

In anticipation of the questions to follow:

I have tried filling it until the PRV opens to clear any debris/sticking PRV (Opens at 3 bar on the nose). No change.

I have isolated the rad circuit at the boiler on the Flow and Return, filled it to normal pressure while off & cold, pressure drops to zero in a couple of minutes. I'm guessing the problem is local to the boiler based on this.

There are no signs of leakage around the boiler, I have put newspaper under the boiler as a drip check and have found nothing.

Does this sound like a simple PRV failure?

Any help appreciated.

 

[idealnumber1]

check blow off pipe outside to see if expansion vessel has gone

 

[JimmyBurnWorld]

Update.

Firstly, the boiler is a CB28X, I was reading a thread about a C27 to see if it was relavent and I posted that model number. Not enough coffee before posting methinks.

I disconnected the PRV outlet pipe and pointed it at a bucket, isolated the rad circuit and filled the boiler to normal operating pressure. The PRV started passing water straight away, just a trickle though, but enough to drop the pressure.

I tried the 'Clicking the PRV' fix, and just my luck, it failed completley!

So, ordered new PRV, due tomorrow, and temporarily 'fixed' the current one to give me heating till then. Ran the heating all day on and off, no problems. Pressure never above 2.25 bar.

 

[JimmyBurnWorld]

Quick update,

New PRV finally made it from Leeds, took 15mins to fit. Job's a good 'un. Been running for two days now on programe morning and night, no problems.