Combining feed and vent to prevent pumpover advice please!

[Rusty89]

Hi all,

A year ago I had a broken gravity fed heating system. I was advised by the good people (@Elkato531 @Johntheo5) here to cut out a section of pipe where cold feed and vent join up in my airing cupboard and replace. I did this, and discarded the pipe which was heavily full of magnetite. New 15mm and 22mm pipes were installed in that section and huzzah, all my problems cured - best feeling on the planet.

However, I get loads of pump over in the loft and the header tank is acting as a radiator. Even when pump speed is on 1. I was advised here to tee the cold feed into the 22mm vent in the loft, which I'm keen to try.

Just a few questions though please gents -

I've got a Vaillant Ecofit Pure boiler - is it alright to do a combined cold and vent on this boiler?

Do I need to install an Automatic Air Vent somewhere?

It's been a whole year of pump over oxygenating my system, would I have corroded that new section up already and need to replace?


Thanks in advance for any advice.

 

[Johntheo5]

Don't think there is any problem with a combined vent and cold feed with that boiler.
I'm surprised to hear your getting that degree of pump over especially after renewing the pipe work.
Are you saying that this cured the pump over and that the problem has returned??

Can you post a photo of your vent and cold feed etc + pump location, the "proper" way is shown below, the pump should be located on the flow from the boiler, so, from the boiler (flow side) you have Vent, Cold Feed, Pump., VCP system.
Will advise on the combined vent and cold feed (like my own) after you post back.

 

[Johntheo5]

Think I have found it here??
Seem incorrect in that the cold feed is before the vent
You seem to have the flow from the boiler going through a magnetic filter then the cold feed then the vent then the pump??

 

[fixitflav]

Can you post a photo of your vent and cold feed etc + pump location, the "proper" way is shown below, the pump should be located on the flow from the boiler, so, from the boiler (flow side) you have Vent, Cold Feed, Pump., VCP system.

I don't get that. Is it pumping downwards? I thought you were a strong advocate of upward pumping! (as am I).
I wouldn't have the vent straight across the top of a tee, that encourages flow up the vent (potential overpumping). I would come off the top of a horizontal section.
I prefer the cold feed up-and-under, to minimise convection warming the F/E tank, encouraging algae growth.

 

[Rusty89]

Here is an updated picture with the sections I cut out and replaced. The cold feed comes in after the vent. I'm pretty sure it goes boiler> filter (why I don't know) > vent > cold feed > loop round to pump, then diverter valve off to CH or HW.

It has been overpumping the entire time, before and after I replaced this section of pipework


Thanks for your replies so far

 

[fixitflav]

You seem to have the flow from the boiler going through a magnetic filter then the cold feed then the vent then the pump??

Partly due to the pipe sizes, I think the photo shows boiler - magnetic filter - vent - pump (downwards) - 3-port valve - cold feed to the HW cylinder inlet.
Sketching it out and putting in some (arbitrary) figures, I'm not surprised it's overpumping.

Editing this - just realised I was looking at it wrong - the thing on the cylinder feed is the manual air release, cold feed after the vent. D'oh!
But what were the changes for? It doesn't look any different hydraulically. Was it just to clean out any blockages in the vent and feed area?

 

[Johntheo5]

Are you sure?, it looks to me like the filter then the vent on the horizontal, then the cold feed below it on the vertical, then the pump.

Anyway I'd be surprised if the combined (like mine, below doen't solve the problem but I would like to see the two pipes the same 22mm diameter.

 

[Elkato531]

Pipe arrangement looks ok to me. The fact that its pumping over implies there may still be a restriction somewhere. How high above this point is the F&E cistern and how high does the vent pipe rise above the F&E before inverting?
If its been pumping over for a year or more, expect the system water to be nice and rusty and the mag filter to need cleaning. A flush would be advisable.
Combining the feed and vent should help. T the feed into the vent (not the other way around) so that there is 22mm vent unrestricted from the boiler to the F&E. I would combine the pipes in the loft space and remove or cap the existing feed connection. While you have it drained, check that section of pipework for blockage again.

 

[cross thread]

You can single vent and feed ,22 mm pipe from bottom of header tank and fit a vent on the old 15 mm cold feed.

 

[Rusty89]

Would it work if I joined them here? Header tank on right off picture, it's raised quite high with the overflow pipe running along the roof and dropping down into tank

 

[Johntheo5]

You can single vent and feed ,22 mm pipe from bottom of header tank and fit a vent on the old 15 mm cold feed.

Like this??

 

[Johntheo5]

The arrangement in post #11 might be your best bet/.

 

[fixitflav]

Are you sure?, it looks to me like the filter then the vent on the horizontal, then the cold feed below it on the vertical, then the pump.

Yes you're right. See edit to my #6.

 

[fixitflav]

Delete post

 

[fixitflav]

It has been overpumping the entire time, before and after I replaced this section of pipework

Strange, specially if the vent pipe is more than the recommended 450mm minimum above the F/E tank top water level. A partial blockage in the elbow between the vent and cold feed could cause it, but you seem to have eliminated that.