Worcester 24cdi - Immediate Rising pressure

Here we go... Its a strange one.

I raised the pressure on a worcester 24cdi to 1.5 bar, and as I closed the the filling tap it immediately rose to 4 bar, and began to spit and boil out of the air filter on the top of the boiler, before locking out.

The PRV does not operate and blow off.

The expansion vessel is fine, with no split and leakage.

Could it be a circulation problem, increasing the pressure when the temp rises because heat inside the boiler can't dissipate?

Im so confused?!?!?

OK when you say the PRV does not operate i take it you mean when the pressure rises?
Have you physically tried to crack the PRV to see if it discharges water outside?
CDI's are prone to trapping sludge in around the drain off under the boiler and if it blocks up the right hand side one this can sometimes clog up the PRV too, but probably quite unlikely as you would have had other problems first usually.
Sounds like your pump isnt working from what im guessing into the situation.
Have you tested the pump is spinning?
Could also be trapped air within the boiler but if you AAV is working again probably unlikely.

Nothing should come out at the top of the boiler.
PRV must operate at about 3 bar, if it doesn't, this could lead to serious damage and danger.
Pressure build up should be gradual.
In a nutshell, you need a RGI to check your system as there are various problems.
Would I be far off if I guessed that the boiler has not been serviced every year as per instructions?

bengasman said:

Nothing should come out at the top of the boiler.
PRV must operate at about 3 bar, if it doesn't, this could lead to serious damage and danger.
Pressure build up should be gradual.
In a nutshell, you need a RGI to check your system as there are various problems.
Would I be far off if I guessed that the boiler has not been serviced every year as per instructions?

Click to expand...

No, it's been serviced every year, it's due next in November.

If the PRV is blocked as previously advised, then it won't blow off.... my worry is that in less than 20 seconds the pressure goes up from 1.5bar to 4bar... and then locks out.

I've already booked my service engineer to come over and check it out... he's coming on Monday.

Thanks for your advice... I just wanted to be ahead of Mr Gasman!