potty potterton pressure dropping

[spaglemon]

just an update

the pressure vessel has been maintaining it's charge but the boiler pressure is still rising and activating the prv not all the time but every single time it has done it it's been when the hot water taps been running , does this point to any part in particular ?

i have replaced the pump now and had to remove and clean the dhw pressure sensor as it was gunked up and was saying the system had low pressure when it didn't , a good clean has sorted that though and the new pump has made the boiler run a lot quieter too

just this problem with the boiler pressure increasing too much when running hot water to sort

any ideas ?

 

[MANDATE]

As you know the water pressure will rise when heating is switched on.
The rise should be around 1bar. It should never be high enough to open the PRV.
Working backwards, pressure must have been 3bar to open PRV.
The rise in pressure must have been well in excess of 1bar, (unless initial pressure was set to 2bar which it should not be)
Can only suggest a recheck. in following order.
Stage 1
With system cold set water pressure to 1bar and disconnect filling loop (mains pressure)
Without using system, observe water pressure gauge over a reasonable period.
Pressure should remain at 1bar.
(1) If pressure drops, then there is leak in system, boiler or most likely PRV not fully sealed.
(2) If pressure rises, it must leak from 'hot water' (mains pressure) through heat exchanger to system water.
The above is to prove whether or not (2) above is part of the problem.
This could mean you set initial pressure at 1bar as required, but this could gradually increase on a day to day basis.
If above is satisfactory then.

Stage 2.
Open PRV to allow discharge.
Confirm water pressure is zero
Check expansion vessel and adjust to 0.8bar
Confirm water pressure still zero.
Close PRV.
Add water through filling loop to 1bar.
Remove filling loop to ensure it has no adverse effect.
Switch heating on and observe max water pressure gauge.
When heating is off observe gauge to ensure pressure drops back to initial setting. ie 1bar.

The above presumes the vessel is the correct size for the total volume of water in the system. If extra radiators have been added without considering the expansion vessel, then this could lead to a problem.

 

[spaglemon]

thanks for the reply , no additional radiators have been added , the expansion vessel is just the stock one which originally came with the boiler

i'll try what you have suggested and will post back the results



thanks