Repressurising the pressure vessel

[B91]

I've just been reading the FAQ sticky on this - all very clear but how would I know this needed doing? My Vaillant Ecomax has been serviced regularly over its five years but I've never seen any of the guys checking the PV pressure. The boiler pressure fluctuates between 1.2 and 0.5, depending on what's running. Is this an indication the PV needs pumping up?

I also have a Santon unvented water cylinder connected to the CH and that also has a PV. The Santon has never been serviced in 10 years or so, so what should I do about that?

TIA

 

[MANDATE]

A expansion vessel needs to be checked and charged when there is no water in it. This means the whole vessel contains air with no water so you have the maximum amount of air for compression.

It is usually charged to approx 0.8bar which is sufficient to push and hold the diaphragm towards the water side.
The following stage is to add water to increase water pressure to 0.8bar. (well maybe 1bar)
The diaphragm under these conditions remains biased to the water side
Now with heating on, volume of water increases, pushes on diaphragm, air gets compressed, pressure of air increases and so does pressure of water.
The rise in pressure would normally be around 1bar.
The opening of the PRV has to be avoided, so pressure must stay below 3bar.
Pressure rises between 1.5bar and 2.5bar or 0.8bar to 1.8bar or anything in between are all ok.
If the expansion vessel is not charged high enough, the diaphragm does not stay biased to the water side, leaving less air for compression and sends air pressure and water pressure too high and activates the PRV
If the expansion vessel is charged too high, the diaphragm may offer too much resistance while the air is being compressed, so again pressure of water goes up and activates the PRV

 

[B91]

Thanks for all that. As neither expansion vessel has been pressure checked AFAIK for several years would you advise that I check the air pressures using the sort of simple gauge you would use to check car tyre pressures? Or, as both CH and the Santon are running fine just leave well alone?

 

[MANDATE]

Checking and adjusting the pressure is to make them operate as they should. As they are operating correctly then what would be gained?
If and when there is any change in the pressure rise and the possibilty of the PRV opening, then the vessel would be the probable cause and then it should be checked.
A car tyre pressure gauge with dial is ideal.

 

[B91]

Thanks. It's just an aspect of the CH that I didn't previously understand at all, but I shall leave well alone.