Combined cold feed and vent

[glenntaf]

Hi

I have always been used to installing central heating systems with the typical H section with cold feed and vent no more than 150mm apart. (As I was taught in colledge and how other heating engineers I have worked with have done it) But recently I have been running into more and more plumbers that are doing away with this and installing a single 22mm combined cold feed and vent pipe. (I have been told british gas do it this way as standard practice) I just wondered how many people have started doing this as routine and for what reason other than to stop pump over on badly designed systems.


Thanks Glenn

 

[glenntaf]

sorry college***

 

[bonzo1974]

I found one the other day and was surprised to see it done that way, I suspect it's for a simpler reason than anything technical - cost! If you can get away with combining the 2 then you save a few metres of 22mm pipe which at about £20 a length will be a decent saving in a housing estate of 50 houses I guess.

I found it was horribly inefficient at filling the system on the F&E tank I saw it done on, as it didn't allow water flow downward and air flow upward easily. I'll definately NOT be doing it myself!

 

[GasmanxxxR1]

I find it runs i queiter when i configure it like this, also stops it sucking in air. Maybe it does take longer to fill but not much

 

[Mike Jackson]

I'll often do this when doing a boiler swap as it prevents pumping over and dragging air in.

 

[buckley plumb]

was told combined feed and vent is a no no at college but chowed the lecturer the suprima manual and he did not know what to say. not found any boiler manual that shows a combined f&v now though so would do as manufacturesr states

 

[Billy Bob Bob]

combined feed and vent was never really recommended by manufacturers because in the event of a boil over it was thought the cold feed could stop it venting over

 

[Millsy 82]

I'll often do this when doing a boiler swap as it prevents pumping over and dragging air in.

If the system is piped up correctly then it should not pump over or drag in air but then when you are just doing a boiler swap you never know what heap you are piping it onto.

I always close couple them and never had a problem before until I got called out to a blocked cold feed the bloke had changed his own pump and put a bigger pump in it only had about 5 ft head and that started pumping over (obviously that was my fault as we all know unblocking a pipe all off a sudden causes a system to pump over) checked with manufacturer converted it to combined cold feed and vent and has worked perfectly ever since.

 

[Nostrum]

Have done it quite often for various reasons, as said its not the best for filling but problem free once running. It used to be recommended for low head installations in quite a few of the manuals. Out of choice I'd have 2 separates, but it has its uses providing the boiler has an over heat stat.

 

[plumb_know]

can i confirm that using this method can stop pump over due to the header pressure from the f+e cistern pushing down on the feed pipe, making it harder for the pump to push back up the feed and over the vent. where if you had the H system there is no pressure from the header tank so it enables the pump to pump over more easily??

i just wanted to make sure my logic was right??