Slow Pressure drop

[trevorbayliss]

My system drops pressure very slowly. It is a vaillant combi and every 6 months the pressure drops to 0.5 bar and so we have no hot water. So i repressurise and problem solved.

The pressure is usually held at 1.5 bar.

I cannot find any leak on the rad valves and have not seen any water in the ceilings from possible leaks in the pipes.

Any idea where the leak maybe and how to find it ?

 

[awph]

If you are only topping the system up every 6 months I wouldn't worry,most pressurised systems will need to be topped up every 6 months or so

 

[mcmoby69]

check the blow off pipe outside to see if its dripping when the heating is at max temp.

this kind of fault is usually avoided by routine servicing. it could be that your expansion vessel is undersized tho, this should have been checked during install.

do a search on this forum as this question has been asked a lot!

quite a simple fix tbh.

 

[ALCPlumbing]

I wouldn't expect it to be expansion vessel issues if you are only losing half a bar or so every six months. Sometimes the AAVs leak slightly. Also you could have a weep on a radiator valve for example.
I wouldn't give it another thought if I were you. Just top it up every three months and you shouldn't ever wake up to a cold house.

 

[trevorbayliss]

Thanks for replies.

I had the same problem in my first house with a vokera boiler and never found the leak. The pressure dropped a little quicker in that place though.

What is the AAV ?

If combi systems ned to be topped up every 6 months or so what is a usual top up amount ? 0.2 bar ?

 

[dominoman]

Thanks for replies.


What is the AAV ?

Automatic Air Vent. Little gadget that installs on high points of the pipes, usually by the pump or cylinder outlet and lets air bleed from the system.

 

[awph]

You should top your system up to about 1.2 bar when cold.The AAV will probably be on top of the pump within your boiler,there are lots of other places where you can loose pressure,somewhere that's always worth a look is the packing gland nuts on your radiator valves.If you pull the plastic head off of the valve it's the nut on top of the valve where the spindle comes through.

 

[trevorbayliss]

Yes i know which are the gland nuts, cheers i will check them.

Automatic air vent will be checked as well.

 

[trevorbayliss]

Update to my last post.

I thought the pressure was maybe a slow drop, but the pressure is now down to 0.5 bar again, so that has been 3 weeks since i last topped up to 1.2bar.

So i do have a leak, but i cannot see any rad which have any weeping nuts or any damp patches in the ceiling.

I have looked inside the boiler and there are no damp patches around the various parts.

I suppose i need to call out and engineer now.

I have UFH in the kitchen but there are no leaks on the separate valve and motor. This has been in for 5 yrs and not had any problem. It cant be likely that the pipe work has got a puncture is it ? It is 15mm and one continuous length.

 

[trevorbayliss]

I have checked the out pipe on the wall and that is dry.

I have checked the expansion vessell and there is no water coming from the valve, just air.

The pressure is 0.75 bar and in the instructions it should be between 0.75-0.9, so it looks as if the exp vessell is ok.

I have decided to turn off the UFH in the kitchen for a week and will see if the pressure drops. If it doesn't it indicates the UFH is the problem i suppose.

 

[gassafeengineer]

I have checked the out pipe on the wall and that is dry.

I have checked the expansion vessell and there is no water coming from the valve, just air.

The pressure is 0.75 bar and in the instructions it should be between 0.75-0.9, so it looks as if the exp vessell is ok.

I have decided to turn off the UFH in the kitchen for a week and will see if the pressure drops. If it doesn't it indicates the UFH is the problem i suppose.

when you say turned off, in what way do you mean?

 

[trevorbayliss]

I mean at the control stat for it. This means the 2 port valves controlling the flow and return shut. So this means this part of my house system is now separated from the main rad system.

In 2 days the system has dropped by 0.3 bar so it is looking like a fault on the house rads.

Can you sometimes have a leak on a system and not be able to find it ? I know where my pipe work runs so cant understand why nothing is showing up.

 

[awph]

Turning off the stat won't isolate the UFH from the rest of the system.You should have isolating valves on the manifold for the UFH,if so then turn those off (as well as the stat).

 

[trevorbayliss]

i see. will do thanks.