Pressure dropping in CH - Vokera Combi

[kevhky]

Hi everyone hopefully you may be able to help

As the title says the pressure is dropping fairly quickly (In a day its gone from 1.5 bar to 0) in the central heating, ive recently done a bit work on a radiator but checked for leaks before i lay the new tiled floor.

Ive done many radiators in my time so im not a newbie to it and fairly confident in doing it

I had to do a couple of solder joints under the floor boards but same again all checked for leaks before overboarding

I added to the rad before filling and inhibitor

Ive checked the ceiling below where the rad and pipes are but no signs of leak

Is it possible my boiler has gone wrong and im obviously persuming its to do with my rad work or could my boiler be at fault

Ive got boiler insurance but reluctant to call them out if its not the boiler at fault

Im goiny to leave central heating off all night ill top it up and see if its dropped in the morning.

Can anyone please let me know if the boiler is possibly at fault

Regards

Kev

 

[Marc86]

first thing i would check is the pressure relief pipe which will be outside the house probably at back of boiler is it dripping from there?

 

[kevhky]

Hi

Ive just checked that pipe and there was a small amount of water inside the pipe ill keep an eye on it

If this is the case whats does that mean could be wrong

Kev

 

[Marc86]

its likely you will need a new pressure relief valve if water is coming out of there, there relatively inexpensive and not difficult to change in most cases.

 

[glasgowgas]

if your prv is leaking, first check the pressure in your expansion vessel

check all FAQS and hints and tips at top of page

check your boiler MIs for model specific operation

 

[kevhky]

Ive also noticed when central heating is running the pressure used to go up to around 3.5 bar when heating was at its hottest it now only reaches around 2 bar

Does this point at pressure releif valve

Kev

 

[glasgowgas]

No it points to your expansion vessel needing recharged/replaced

 

[kevhky]

if your prv is leaking, first check the pressure in your expansion vessel

So if the pressure is incorrect in the Expansion vessel would this cause ch water to exit via the prv

kev

 

[petit_pablo]

if your prv is leaking, first check the pressure in your expansion vessel

So if the pressure is incorrect in the Expansion vessel would this cause ch water to exit via the prv

kev

Correct.

The expansion veesel is there to take up the expansion of the heated water as the system. If the expansion vessel is flat there is nowhere for the heated water to expand into so the pressure increases. Once the pressure reaches around 3bar the pressure relief valve begins to open up to reduce the pressure build up. The pressure then drops down when cold, you refill the system and the cycle starts again!

To remedy it, repressurise the expansion vessel( its down the back) as described in FAQs and then replace PRV before refilling

 

[kevhky]

Very good information there thanks to everyone

Ive checked inside the pipe that goes outside and looking in i can see what looks like either sludge or mud / muck not sure what it is, could i turn the fill loop on so pressure rises above 3bar so the water will then flush out the pipe

is this safe to do or is there another way to do this other than poke something in

Kev

 

[petit_pablo]

Very good information there thanks to everyone

Ive checked inside the pipe that goes outside and looking in i can see what looks like either sludge or mud / muck not sure what it is, could i turn the fill loop on so pressure rises above 3bar so the water will then flush out the pipe

is this safe to do or is there another way to do this other than poke something in

Kev

I wouldnt worry about whats in that pipe, it should be dry in normal operation

 

[kevhky]

I wouldnt worry about whats in that pipe, it should be dry in normal operation

Hi and thanks for the advice

I cleaned out the pipe and yes there was water in it (not sure if this is a collection of rain water over a period of time though so im keeping an eye on it

Last night i topped the system up to 1 bar switched off the heating and when i checked this morning it had dropped to just belw 0.5 bar

Does this mean i must have a leak in my pipework or still could the boiler be at fault as i would have thought if it were in my pipework the pressure would have dropped to 0

When the heating is running the pressure does seem to drop within 2 - 3 hours

Hope this helps in solving my problem

Thanks for your help

Kev

 

[petit_pablo]

Put a sandwich bag over the end of the pressure relief pipe outside and secure it with a cable tie/elastic band. Fill CH system up and see if water collects in bag.

After the pressure relief valve has opened once, they usually dont sit back down on the valve seat properly and allow a small amount to pass through

 

[kevhky]

Put a sandwich bag over the end of the pressure relief pipe outside and secure it with a cable tie/elastic band. Fill CH system up and see if water collects in the bag

Hi again

After a day the bag has collected a small amount of water possibly enough to fill an egg cup

To me this doesnt seem very much, this afternoon im going to drill a couple small holes in ceiling below just to double check nothing is leaking in the pipework above i recently carried out although im certain it isnt.

Could the water be escaping elswhere within the combi, (into water supply, evaporating when ch is running within the combi) im just pulling at strings here mind

Thanks anyway everyone

Kev

 

[MANDATE]

Hi again

After a day the bag has collected a small amount of water possibly enough to fill an egg cup

To me this doesnt seem very much

Kev

Why not drain an egg cupful of water from a radiator and see how much the pressure drops.
Your PRV is letting water pass due to dirt on the seating face.
When the heating is on, the pressure rises by about 1 bar and water will escape at a faster rate.
Your options regarding the PRV are (a) open it manually to see if it improves (b) dismantle it and clean the valve seat/rubber washer or (c) replace the PRV with a new one.
Now you need to consider why the PRV opened in the first place?
It is almost certain the expansion vessel has leaked some air out like a car tyre does over a period of time. The volume of air will have been reduced to such an extent that compressing what remains would increase the pressure rise enough to open the PRV.
You need to check the air pressure in the vessel and correct it before dealing with the PRV