boiler - high water pressure problem

[wood butcher]

We have a Ravenheat 820 fanned combi and I noticed the other day that the water pressure was nearly at 3bar. I searched the internet and from what I read I began to suspect that the expansion vessel (EV) was where the problem lay. I pressed the "tyre" type valve on the EV and water came out (I hoped to find air but was disappointed that it was water - the water only dribbled out and then appeared to stop quite quickly). From what I have read I suspect the EV is goosed and that my easiest option is to connect a new external EV.
However, we have been in the house six years and I was wondering if the EV may just have lost its charge over the years and that I should perhaps recharge the existing EV before deciding on a new one.
Am I right in thinking that to recharge the existing EV I should turn off boiler and reduce water to zero by bleeding a radiator before carrying out the recharging process (which I understand is to connect foot pump and pump to MI 0.5bar).
I have read various threads and one thread suggested that the boiler should be isolated and the system drained down before recharging. This has confused me because as I understand it we have a sealed system and if the pressure is reduced to zero then there would be no resistance to the recharging process - but having said that, there might be someting I am missing.
In the meantime I have turned down the heating thermostat knob as a means of reducing the heat in the system and hopefully thereby reduce the water pressure. The boiler cuts out/reaches temperature when water pressure reaches about 2.7/2.8bar so as far as I knkow the PRV has never operated
Your thoughts/comments would be appreciated.

 

[tamz]

Recharging it will/may work for a little while but it will probably need replaced. Dropping the pressure will be ok but it is hard work pressing a foot pump with your hands. It takes a lot of pumping. Much easier if you can borrow a small compressor.

 

[mountainman]

Water coming out of the tyre valve of the EV indicates that the balloon in the vessel has perforated, pumping it up will have no effect so you need a new Expansion Vessel.

 

[Simon F]

:iagree: need a new expansion vessel.
If the vessel on the boiler is not leaking it is possible to leave it in place and fit an external pressure vessel
( assuming there is room for this ) best to call a local gas engineer and get the job done properly, shouldn't be to big a job, assuming nothing else is wrong with the boiler.

 

[wood butcher]

Thanks guys for your replies.
I was thinking that repressurisation of the existing EV was probably going to be a temporay measure but given the presence of water then the need for a new EV was the most likely way forward.
Regarding the pressurisation - am I right in thinking that if the diaphram/balloon was intact then I would be pumping up a small portion of the EV (ie. the "air" side of the EV). And if the diaphram/balloon was split I would be pumping up the complete system which would include the flow and return pipework. My question is - would the pumping up of the "complete system" show as a rise in the water pressure guage?
It might be that case that the pumping up of the "intact" diaphram/balloon would also show as a marginal increase in the water pressure guage. What I am trying to get as is - if, while I was pumping up the EV, I noticed that the water pressure guage was rising as I pumped - would that be proof positive that the diaphram/balloon was split?

 

[gassafe]

you need a new expansion vessel as already mentioned.

 

[sheff paul]

with a 6 year old ravenheat maybe older i would be tempted to fit a new boiler

 

[tamz]

The system pressure rises because you are pushing a couple of gallons of water out of the ev back into the system. If is is a tiny hole in the diaphragm it may last a week or so, anything bigger and it will be flat by tomorrow. You will need to replace it.

 

[wood butcher]

Thanks for everybody's input.

I think I will give the repressurisation a miss just in case it makes a pin hole in the diaphram into something much worse.
I will organise an external EV and hopefully things will settle down. 'Tis a fact that I am beginning to think that the old boiler is getting on in years - i might trade her in and get a new one.
Might also get a new heating boiler.
Thanks guys