Grant oil combination boiler

[HAH]

Hi,

I've just joined this forum as I'm having problems with my oil combination boiler. Everything works fine but continually need to keep bringing the pressure up using the loop 2 - 3 times a day. I thought there must be a leak somewhere but all pipes etc are bone dry.

Can anyone help?

Howard

 

[Burnerman]

Check outside to see the pressure relief valve pipe isn't running....on a Worcester I looked at today, the automatic air vent was weeping constantly.
Just edited this post.....the AAV doesn't cause the dripping outside - 2 separate events.... in my case. If the expansion vessel has had it, it won't allow any more expansion of the hot water, so the PRV will discharge to outside. J

 

[martineire]

Expansion vessel is more than likely the prob and needs replacing. check safety valve its probably blowing off water due to faulty expansion vessel, safety valve should be piped to outside

 

[HAH]

I have just checked the outside pipe (I assume from the safety valve) and it's dry. Could the expansion vessel still be the problem? I know the vessel should be pressurized to 1 bar, can it be checked and filled if necessary with a foot pump?

many thanks for the replies

Howard

 

[Burnerman]

Ideally the CH system should be depressurised before you check and pump up the EV.....10 psi is a good starting point if you dont have manufacturers info. A car or bike pump is fine. If you press the air schraeder valve and water squirts you in the eye, the diaphragm within the EV is split. John

 

[HAH]

Need to get myself a new foot pump so I'll let you know how I get on.
If the expansion vessel is pressurized and therefore not causing the problem, any idea what else might be wrong?

Many thanks for your help.

Howard

 

[Burnerman]

If the EV proves to be OK and the pressure is still dropping, I'm afraid there is a leak somewhere....and if you are filling up several times a day it has to be significant, unfortunately. John

 

[HAH]

Hi John,

I think the EV is okay but ordered a new foot pump to confirm. There was the slightest dribble of water when I pressed the schraeder valve but that's all. It is now bone dry. I have (using a very old pump) managed to pump the EV up to 1 bar (i think, gauge is faulty) and the pressure gauge on the boiler rose to .5 bar. Does that make sense?

I believe when checking the air pressure in the EV the water should be cold and the system pressure reduced to zero. How do I reduce the system pressure?

Thanks
Howard

 

[martineire]

when your heating system is full press the schraeder valve if water comes out of valve your EV is shot and you need to replace it, if no water comes out your EV is ok and you have a leak somewhere else. To check the pressure of your EV you need to drain down the heating system first and only then check with pump and pressurize if required. there should be a drain off on your boiler to drain the system and a filler loop to refill the system on your grant combi. Look at your boiler manual if you still have.

 

[Burnerman]

Imagine the EV to be a steel box, split down the middle courtesy of a rubber diaphragm. There is air on one side - the one with the schraeder valve - and water from the CH circuit on the other. Ne'er the twain shall mix! If you get any water at the air valve then the diaphragm is porous or split.
When you buy a new EV, there will be about 10 psi of nitrogen in it. Use a car or bike pump to pressurise up to the manufacturers recommendation if necessary - air is 80% nitrogen, after all.
So, if the water side is depressurised, the diaphragm is displaced towards the water fill pipe due to the air pressure within. When the CH is repressurised, the diaphragm then moves to a position where it is held with maybe 1.5 bar of water on one side, and air on the other. So, as the CH water gets hot and expands, the diaphragm deflects more towards the air side and the pressure gauge rises a bit....if the pressure gets too much then the PRV opens, venting water to the outside for safety.
So, if you press the schraeder valve and water hits you in the eye, the diaphragm has allowed water to be on the wrong side of it, and you need a new one. John

 

[martineire]

air is 80% nitrogen,

Air is made up of 78% nitrogen other than that your spot on

 

[HAH]

Thank you both for taking the time to explain things. Your very full explanation John of how the EV is made up and how it works has finally sunk in. I should at least now be able to determine for sure whether or not the EV is serviceable.

Many thanks again

Howard