System pumping over

[picasso]

The problem is where the pump is in relation to the vent/feed, if the pump is after the vent/feed it cannot suck air in or push water back up the vent.

 

[iep]

Understood.

We were planning a new boiler for early next year anyway and that would definitely require the pump to be moved. So it's no great hassleto do it now and renew the ancient pump and valves while I'm at it.

Thanks again.

iep

 

[iep]

Hi Picaso. I can understand why the pump is unable to push water up the vent if it is located after the vent pipe (negative pressure and all that).

However, I would have thought that it is more likely to suck air down the vent in this location due to the neagative presure at the vent pipe?

Again, not doubting the advice, just tryingto understand.

Cheers,

iep

 

[picasso]

View media item 28358
this is how your system should look, as you can see the pump cannot pull air down the vent pipe unless the cold feed is blocked, if the pipework is in good condition might be worth sealing it.

 

[onlyfitidealboilers]

it shouldn't suck in air as the cold feed is fitted in between the pump an open vent, stoping the pump sucking down on the open vent.

thats why it is very difficult to have the system sucking in air if its combined vent/feed, the only way it can suck air if its combined is if you dont have the head between pump an tank an if it does pump into the tank if the water bubbles when hot when it cools down air will be drawn into the system.

 

[iep]

Guys, thanks for those posts.

I finally understand why we have a vent and a cold feed. The cold feed is the neutral point and this isolates the vent from the pump. That has been bugging me for ages and I now get it.

onlyfitidealboilers, do I take it then that the combined vent/feed is a common trick? The solution I am proposing actually does away with the vent entirely:

Untitled

• iep
• 22 Nov 2010
• 1

Is this a combined vent/feed or something else again?

Cheers,

iep

 

[iep]

Answered my own question by doing a search. This is a form of combined vent/feed.


Cheers,

iep

 

[hagi]

 

[iep]

The boiler manual refers to an overheat stat and, in fact, it triggered last winter when an air lock formed after filling (so I know t works). I guess it needs one since it can be used in a sealed system?

I'm happy for water to surge up and down the combined vent/feed since it shouldn't become airarated in the process.

Cheers,

iep

 

[onlyfitidealboilers]

that is why its called a feed & EXPANSION tank! that is where the hot water will go as the oxygen in the system expands.

the water level in the tank should not rise too much only very little.

also cheak the level of the water in the tank when cold, isnt more than say 4 inchs

 

[iep]

I'm waiting for Glowworm to get back to me with definitive advice on whether the energysaver60 can be used with a combined feed/vent and then hopefully I can get it installed and put the pump over and related system corrosion issues behind me.

Thanks again to all.

iep

 

[D_Hailsham]

that is why its called a feed & EXPANSION tank! that is where the hot water will go as the oxygen in the system expands.

It's the water expanding which causes the level in the tank to rise, not the oxygen.

the water level in the tank should not rise too much only very little.

The expansion is approximately 4% of the volume of the water in the complete system when cold. So if you have 75 litres, it will expand by 3 litres

also check the level of the water in the tank when cold, isn't more than say 4 inches

Make sure that the float valve in the F/E tank opens before the water level reaches the outlet at the bottom of the tank.

 

[mickyg]

wouldnt personally fit a combined feed and vent as a single pipe. It can prove a real nightmare for filling and draining.
best way is to keep the vent and tee the feed into the ventlike so
View media item 21723

 

[neiln]

Swap the pump round
swap the 2 port valves round
swap the flow and return on the cylinder
and change the boiler pipework as per drawing

Untitled

• neiln
• 22 Nov 2010
• 1

 

[mickyg]

Swap the pump round
swap the 2 port valves round
swap the flow and return on the cylinder
and change the boiler pipework as per drawing

i will be a lot less work just to move the pump.