Ravenheat Boiler Losing Pressure Daily

[ronniedolphintrainer]

Hi all,
I'm looking for a bit of advice - we had the Ravenheat CSI 120T Low Nox Combi installed about 12months ago. Initially all was fine and we got to the summer having to top up the pressure a couple of times but didnt think much about it. After the long hot summer (OK maybe not!) we are now using the heating more and have to top up the pressure every day, sometimes twice a day to 1.5 or the whole thing shuts off when it gets below 0.4.

With that much water leaving the system I thought leak, but with a newly fitted laminate floor throughout the ground floor of the house I dont particularly want to take it up to look, and I cant see any signs of one from upsatirs. I've had a quick scan through the old posts and there are mentions of PRV problems and Expansion Vessels which need more air, so I'm hoping its something like that rather than an underground leak.

I guess my question is, not being a plumber, are there any easy checks I can do myself to see if it is a problem with the actual boiler or wether it is a leak in the downstairs pipes?

Many thanks, and ideas/suggestions gratefully received!

 

[kevplumb]

check the prv (outside) first

View media item 16652


what's the pressure cold and hot

 

[MANDATE]

The size of a expansion vessel is related to the total volume of water in the system and the extra volume when it gets heated.
As the volume of water increases the volume of air in the vessel decreases as it gets compressed.
As the air gets compressed it pressure increases along with the water pressure.
The vessel matched to a system will accommodate about 1bar rise, but there is also a PRV to set to 3bar to take into consideration.
So in operation 1bar to 2bar or 1.5bar to 2.5bar is normal.
If the volume of air in the vessel gets halved, then the pressure basically gets doubled. So the 1bar to 2 bar, becomes 1bar to 4bar. PRV opens pressure drops to almost zero and you add more water and repeat the process over and over.
Its possible the diaphram in the vessel is ruptured, but more likely its lost some of its 'air pressure' charge.
So depress the valve on the vessel to make sure no water comes out.
You need to reinstate the air pressure (foot pump and pressure gauge), but remember the vessel is full of water and that has to be discharged or drained to ensure you have a vessel with max 'air' capacity.
The only problem is that PRVs once opened don't usually seal properly and you may find that you still lose pressure, but for a different reason.
securing a plastic bag to the outlet pipe will collect the water if it's been leaking over night.
Also I would suggest setting water pressure when cold at the lower end. Starting with 1bar is less risky than 1.5bar

 

[kevplumb]

and there endeth the first lesson

good post mandate

 

[ronniedolphintrainer]

Thanks Kevplumb and MANDATE - I was going to try the bag around the outlet last night but thought better of it with the weather warnings, so I'll try again tonight. Great post - I'll let you know how I get on!