Ait in my hot water system

[ma6mkd]

I have my hot water cylinder HWC in the loft. We have a power shower and we find we are always getting air in our system and have to purge it out.
The shower comes off a surrey flange in the top of the HWC and air is sucked in from the vent.

So I assume the HWC is not filling fast enough. We have only about 100mm
head and a 22mm feed into the HWC from the CWT.

I am planning to put in an additional 28mm feed from the CWT to the HWC but also wondered if I extended the vent pipe, which is positioned over the CWT, so the the end was submersed in the CWT. I assume air couldn't then be sucked in. But what other problems might be caused if I do that?

Mark

 

[Nige F]

You`ll get slugs of cold water in between the hot ...the other idea of the 28 feed is a good one

 

[Tipper]

Is there a horizontal run between the HW cylinder and the pump?

This can collect any air in the system and lead to air locking of the pump.

I found that ensuring there is a continual gradiant 'back' up to the cylinder cured the problem in my last house. Alternatively you could try fitting an automatic air release to any horizontal run.

 

[ma6mkd]

Thanks for your replies. My pump is about 1 foot below the base of the HWC. I don't have any horizontal runs. We have solar panels on the roof and a mixer valve has been incorporated to mix in cold water if the water is too hot going to the shower. ( Although we have a thermostatic mixer shower cartridge fitted)
If we made the vent longer by perhaps looping it a few times would that help as well?

 

[TicklyT]

You've 'turbocharged' the hot feed to the shower, so now you will need to 'race tune' the cold inlet to keep up with it!

It doesn't really matter how far up, down or sideways the vent runs - as soon as the outlet flow rate overtakes the inlet flow you can achieve with 100mm of head, it will draw air down the vent. Anything to stop air being drawn down the vent stops it qualifying as an open vent, and may lead to the cylinder either collapsing or bursting.

 

[ma6mkd]

Thanks, I suppose a horizontal HWC would help by increasing the head. But that is a BIG expense.

 

[Nige F]

Not necessary . It`s as Tickly T says .. get that 28mm feed in Instead of the 22 NOT as well as and see how that helps

 

[ma6mkd]

Thanks for your suggestions. I will try the 28mm feed instead of the 22mm
and see /hope that that race tunes the HWC fill to keep up with the power shower.

 

[Agile]

I seem to remember that there was a BS that stipulated a cold feed to a hiot cylinder should always be 28 mm.

Tony