potty potterton pressure dropping

[spaglemon]

i have a potterton puma 100e and last week the prv activated

a friend of a friend took a very quick look and said it could have been an air bubble making it's way out which caused the pressure to spike and activate the prv ?

i then noticed that the pressure was slowly dropping and suspected the prv needed replacing thinking that it might not be sealing properly after letting go

i fitted a new prv and while the system was drained i checked and re-pressurised the expansion vessel which had lost some pressure

after re-filling and bleeding the system the pressure is still dropping (approx 1/2 to 3/4 bar over 24 hrs)

no visible leaks or dripping taps to be seen and no water coming from the copper pipe on the side of the house



any advice gratefully received

 

[misterdubya]

Ok,

Firstly it sounds at though you have a leak or your new PRV has activated and not re-seated. This is unlikely, unless you have not re-pressurised your expansion vessel correctly. The leak could be within the boiler and evaporating - hence you not finding any drips etc.

Secondly, from your other thread, you wish to replace the pump. Why is that?

Mr. W.

 

[spaglemon]

i've been meaning to replace the pump for some time now as it's been getting pretty noisy , have tried bleeding it from the centre bolt to no avail and have now ordered a new pump

the new prv has not activated and i pumped up the expansion vessel to just over 1 bar as stated in the potterton instruction manual while the system was drained , does this sound right ?


thanks

 

[MANDATE]

Suggest the expansion vessel is rechecked.
Could be slowly losing air charge through the schader valve.
If the air pressure is reduced the water takes up more space in the vessel.
This results in the water pressure going beyond the normal 2 or 2.5bar and opening the PRV.
What are the pressures before heating is switched on and what pressure does it increase to?
The pressure has to increase to 3bar to operate the PRV and a escaping air bubble does not increase the pressure, it reduces it like when bleeding radiator

 

[spaglemon]

i'll check and get back to you



thanks

 

[spaglemon]

sorry do you mean the pressure difference in the expansion vessel or in the central heating system pressure ?



thanks

 

[bengasman]

i have a potterton puma 100e and last week the prv activated

a friend of a friend took a very quick look and said it could have been an air bubble making it's way out which caused the pressure to spike and activate the prv ?

Not a chance.

after re-filling and bleeding the system the pressure is still dropping (approx 1/2 to 3/4 bar over 24 hrs)

You got a leak somewhere.

 

[MANDATE]

I meant the pressure difference in the heating system.
The rise should be around 1bar.
As the water heats up, it expands. The extra volume is taken up in the expansion vessel and compresses the air. (providing there is sufficient capacity).
Compressing the air increases the air pressure keeping both air and water in equilibrium, so the water pressure is also increased.
The total volume of water in a system, dictates the size of a vessel needed to allow for the expansion.
So a correct sized vessel that is partially filled with water, is the same as having a under sized vessel.

 

[spaglemon]

the difference between hot and cold was a little over 0.5 bar , the pressure vessel seems to have dropped 0.5 bar since yesterday !

when i was waiting for the boiler to cool down i attached a footpump to the expansion vessel to double check the pressure , i then switched on the boiler and removed the pump from the expansion vesselwhich possibly lost a bit more pressure in the process , the boiler pressure then began to increase rapidly and before i had a chance the new prv activated along with the vent at the top of the boiler

as the expansion vessel appeared to be losing pressure i have just replaced the schraeder valve and have pumped it up to 1 bar , i have left the footpump attached and will monitor it over the next few hours to see if it drops at all , i'm not convinced the seal between the footpump adaptor and the valve will be 100% but if i remove it and then re-attach it later to check if the pressure has dropped there is bound to be some air lost in the process and it might make it appear that there's a leak in the vessel ?


if it does drop does that definately mean a new expansion vessel will be needed ? if so where's the cheapest place to get one ?




thanks again

 

[spaglemon]

and how can i find out what capacity the stock vessel is ?



thanks

 

[misterdubya]

You may need to plumb in an external vessel, plugging off the old if it wont hold its charge. Unless you want to take the boiler off the wall that is.

Mr. W.

 

[spaglemon]

not sure but it looks like i could get it out to replace it without taking the boiler off the wall , but i may very well be wrong , hopefully someone has done this job on this boiler before and knows



thanks

 

[misterdubya]

Check the commincation tube for blockages if your fitting a new vessel onto the boiler.

I thought the boiler had to come off, but I may well be wrong.

Mr. W.

 

[MANDATE]

I don't know if using the foot pump to check the pressure is a good idea?.
Also I think it's better to over inflate and check with 'push on' gauge, then reduce to the desired pressure
The fact the PRV has opened means the vessel was partially full with water.
Just increasing the air pressure to 1bar is only half of the requirement.
The more important bit is making sure the vessel is empty of water.
So when inflating, there must be somewhere for the excess water to be discharged to.
I doubt if the vessel needs changing unless there is evidence of the flexible diaphragm being ruptured. If the valve is depressed and water discharges then 'yes'
Regarding vessel size, Is it not possible to measure and calculate the volume in cubic centimetres

 

[spaglemon]

when i recharged the vessel i left the drain plug off and as i pumped up the vessel more water came out of the drain point , i then re-filled the system and pressed the valve on the vessel and there was no evidence of water coming out at all , i drained the system again and then recharged the vessel to 1 bar and refilled the system , now been running happily for an hour or so , have bled all the rads and will see what happens over the next few days

will keep you updated


thanks