DIY Requesting Advice For Open Vented Hot Water System

[Richard at Home]

Hi

I was hoping someone could pass me a little advise please

I have a STD open vented hot water system with a hot water tank and a large cold water tank in the loft

this is the problem i have and i am trying to find a way to resolve it

The cold water tank is at least 15 foot above the Hot water tank

28mm Cold water feed to the bottom the hot water tank

This is the problem


If i run off the hot water in the bath 22mm it appears that the water flow seems to exceed the pressure of the cold water feed pressure and air is sucked into the pipe work while running the hot water off.

This does not cause a major problem. does not stop water flow but its just a pain to be honest. you can see the air in the hot water as the bath fills.

Turning the flow of the hot water down reduces the problem significantly.

it is as though the flow rate of the hot water goes into siphon flow creating a negative pressure against the main vent inlet and just drags air into the system.


This then places an air lock in the hot water feed the next time the shower pump kicks in that i know is not good for the pump


I know this is not the solution but it is how i found the route cause

If i place a Temp seal over the Air Vent pipe wile running the bath the problem is resolved. Obviously this was removed after experiment.

I cannot raise the height of the vent pipe any more as it is high in the loft as it is.

We can not use a combo system as the mains water pressure is very poor into the property


I just wondered if there are any options or subjections anyone could make that i may have missed

Thanks Everyone.

Best Regards

Richard

 

[Carnegstar]

One way valve on the vent pipe?

 

[Mike Jackson]

One way valve on the vent pipe?

Do not under any circumstance follow this advice, there should be no valves on the open vent which should rise continuously from the cylinder to the storage cistern. This could cause the cylinder to implode.

This is most likely to be a pipework configuration issue. A picture of the pipework layout in the airing cupboard would help.

 

[diamondgas]

:iagree: DO NOT valve off the vent!!!! Sheeeeeeeeeeeeeeeeeeesh!!!

In my opinion you have a feed issue. 1st thing I'd check out is that the fold feed isolation valve is fully open. If the water is being drawn off quicker than it is being replaced then the level of water in the vent will drop and air will be drawn in. In my opinion your issue lies between the tank in the loft and the tee for the vent/draw-off! There could be a scale build up on a fitting ........?

 

[Richard at Home]

Hi All

Happy new year

Just thought i would give you an update on this post

I cut out the old vent pipe that while i was cutting it out i could see was way to close to the power shower intake pipe

I installed a 22mm surrey valve on top of the tank and ran a new vent pipe into the main cold water tank

100% problem resolved no more air in hot water system and power showers

Thanks everyone for your feedback

Regards

Richard

 

[turnpin]

Thanks for letting us know as it may help someone else as Mike Jackson stated most likely cause pipework layout ....Happy new year regards turnpin

 

[stevetheplumber]

nice to get feedback thank you