Pumping over on vented system, despite cleaning, new pipework and ..

[Coddey]

… praying to the plumbing God, Bob

Pictures and layout details attached, so be patient.

21 year old oil fired system in pretty good nick. I noticed some minor pumping over from the vent (occasional burst of water, and the odd dribble). Didn’t think much of it as I was about to replace the heating pack, clean the system with F3, and check the cold feed all at the same time.

I noticed the start of some magnetite in the cold feed, so isolated the pump, cut out the infected pipe and replaced (circled Red on pic). At the same time, I cleaned out the tank, all the rads and then flushed through the whole system with F3. After I fitted the new 2 port valves, I added a Fernox TF1 Omega filter in the return pipe for a belt and braces solution.

All went back well, system works a treat……..except the pumping over is still there.

The boiler is in the kitchen, the pipework goes into the loft (Bungalow) along the loft space for around 2 metres, then into a 22mm air separator with vent on top, cold fed tee afterwards (approx. 8cm between the vent and cold feed). Then drops down around 1.5 metres into the airing cupboard and enters the pump (original pump since 2002, no known issues from previous owner). After which into heat / water valves and off under the floor to the rads. From floor returns up through the airing cupboard via the TF1 then along the loft space back into the boiler (there is an AAV fitted on this return, and on the top feed coil to the hot water, both of which were replaced as they really help bleed the system when refilled!)

Distance from vented elbow to water level in tank is 460cm. I’ve tried adjusting the ballcock to lower the tank water lever, turning the pump (Granfos Alpha variable speed) on its lowest setting, the pump over still happens. I’ve looked down the pipework into the bottle air separator with a borescope looking for blockages, nothing found.

Property next door is exactly the same, the same system, the same layout, the same original parts. It doesn’t pump over.


Ideas on a postcard?

 

[ShaunCorbs]

Tbh I wouldn’t even mess around with it it’s a bungalow so not much head on the vent you could extend this but I would just seal the system eg get rid of the f and e tank and put an expansion vessel prv and filling loop in etc

 

[John.g]

A combined Vent and cold feed like mine will almost certainly cure that problem and remove that air eliminator.

 

[Coddey]

A combined Vent and cold feed like mine will almost certainly cure that problem and remove that air eliminator.

That indeed is the vent and cold feed. I cut into the cold feed pipe to check for debris before draining hence the isolating valve (that was later removed with the associated pipework) .

I would love to close the system, but the rads are old and I doubt would survive.

So, I remove the air eliminator and reconnect to the cold feed Tee, then add the vent on top of the cold feed into the tank? I've never seen one done like that before, but then again I'm not in the trade lol

 

[John.g]

It possibly would work by doing it that way but it almost certainly will if you combine it high up, maybe not exactly like my 50 year old system from new but I would suggest teeing it in as high up as possible, near the F&E tank, I would then install a isolating valve on the cold feed to the ballcock and then fill the system very slowly so as that air can escape up the same pipe as the cold water is flowing down, I don't have any problem filling mine that way and with no automatic or manual air vents.

 

[Coddey]

It possibly would work by doing it that way but it almost certainly will if you combine it high up, maybe not exactly like my 50 year old system from new but I would suggest teeing it in as high up as possible, near the F&E tank, I would then install a isolating valve on the cold feed to the ballcock and then fill the system very slowly so as that air can escape up the same pipe as the cold water is flowing down, I don't have any problem filling mine that way and with no automatic or manual air vents.

I just re-read my post and it doesn't make sense to me now .

I meant to say remove the air eliminator and reconnect the pipe to the pump feed / fill tee. Then replace the 15mm cold feed pipe with 22mm and place the vent on the 22mm cold feed pipe at the point it enters the F&E.

 

[John.g]

Just to be clear, the cold feed refers to the pipe coming from the bottom of the F&E tank, so replace the air eliminator with a 22mm T, reconnect the 22mm vent into the top of the T and then connect the cold feed (preferably in 22mm) into the vent where it rises up past the F&E tank with another T. Then, at some stage install a 15mm isol valve on the mains makeup to the F&E tank ballcock.

 

[Coddey]

Just to be clear, the cold feed refers to the pipe coming from the bottom of the F&E tank, so replace the air eliminator with a 22mm T, reconnect the 22mm vent into the top of the T and then connect the cold feed (preferably in 22mm) into the vent where it rises up past the F&E tank with another T. Then, at some stage install a 15mm isol valve on the mains makeup to the F&E tank ballcock.

Yep, that's what I meant (as per attached drawing). I was just going to fit the vent as per yours on top of the cold feed. I've already fitted an iso valve to the mains coming into the tank to aid cleaning it.