Loss of water pressure from hot water expansion tank

[nick]

I have recently had a new 8 litre capacity Zilmet expansion tank fitted to my hot water system. The water pressure in old tank started to build up until water started leaking through the seam around the circumference and the diagnosis was a faulty tank. Before this started happening, I had noticed I had to top up the water pressure quite regularly as it kept dropping gradually nearly to zero bar. I always tried to keep it above 1 bar when cold.

Now with the new tank, the water pressure is still dropping gradually over a period of a few days. The hot water system was partly drained to install the new tank, so I thought this might just be settling down. I have checked for radiator leaks and have not been aware of any water damage from anywhere particularly.

I am worried if the new tank has been installed correctly, particularly if the air pressure in the bottom half of the tank has been set correctly as I have read if incorrect the diaphragm will not work properly. If the air pressure is wrong would this affect the water pressure in the top half or is there just a leak from somewhere I have not noticed?

I would really appreciate any advise from someone who has experienced this.

Thanks

Nick

 

[diamondgas]

nick ... you talking about the pressure on your central heating boiler gauge or the pressure on an unvented hot water cylinder gauge? It sounds like you may be getting the two systems confused, I don't know?

 

[nick]

Hi Steve...it is the water pressure gauge on an unvented hot water cylinder. I was talking about the radiators because with the gradual loss of water pressure I assumed a radiator or something might be leaking?

 

[AmritPedersen]

I'm with Diamondgas, in that I'm not clear if you're talking about the central heating system or the hot water system. As you say you had to keep topping the system up, I'm assuming you're referring to the central heating side.

OK, the simple things can be the PRV valve letting by (check if the outlet is dripping), this could have some crap from the system keeping the seal slightly open. If your EV had failed, then your system would dump the pressure build up thru the PRV.

Of course you could have a leak in the system (everything upstairs should be easy to check - moisture around fittings/rads, stained ceilings etc. ground floors are harder to check, unless the pipework is surface run).

It could be that the new EV is simply too small for the job or (as you suggest) have the incorrect pressure.

I've heard of a leak in the primary heat exchanger escaping through the condensate pipework, resulting in a pressure loss but no visible signs of a leak.

I'm sure there are more possible reasons I can't think of at the mo.

Good luck

 

[nick]

Thanks for suggestions Amrit. I will check at the weekend.

You mention EV possibly having incorrect pressure. Are you aware if the air pressure is incorrect this could cause a loss of water pressure in the EV?

Cheers. Nick