Some Muppet Disconnected the Expansion Pipe!!

[Plumpplumber]

I'm in the process of sorting out a CH system in my sister's house. She moved in recently and I'm going to move some radiators for her. To my horror I've found the expansion pipe has been cut just above where it was connected to the system and what appears to be an automatic air vent added in its place!

I've attached a PDF of the existing layout - looks like it was originally a gravity feed to cylinder then changed to a fully pumped system with two motorised valves. To my mind though it looks lethal and I'm surprised it even works at all.

Could someone please have a look at the PDF and advise how best to reconnect the expansion pipe, while retaining the two valves. I don't think simply reconnecting the expansion pipe in place of the air vent is the answer because with the HW valve closed the heating system would have no expansion point.

Would connecting the expansion between the HW valve and pump be better or does that risk pumping over the head? Would tee-ing in between pump and boiler be better?

Any suggestions or advice greatly appreciated!

 

[Rckape]

If the feed from the tank is still there then the system still has somewhere to expand to. Even so, I would reinstate the expansion pipe and remove the AAV as its not required. Any air the AAV would remove will go up the expansion.

 

[Plumpplumber]

That's what I'm planning - just wondering where exactly to tee it in because if I reconnect to the original point it will be isolated when the motorised valve to the cylinder is closed. Would it be better tee-d in between the boiler and the pump/valves so that it is never isolated regardless of whether there is flow to rads or cylinder.

Another possibility would be to reinstate the expansion pipe to the original point and return the cylinder circulation to gravity with the motorised valve moved into the return instead of the flow (leaving the expansion connection on the flow open to the boiler even when the cylinder is 'satisfied'.)

Which would be the better option?

 

[Chalked]

Don't reconnect the vent where it was. It will pump over like s good un!
Either leave it like it is. ( it's ok) or alter the pipework snd fit an air separator.( air jec etc) before the pump.

It will expend up the cold feed and the new boiler will have a safety overheat, so no danger.

 

[Plumpplumber]

Don't reconnect the vent where it was. It will pump over like s good un!
Either leave it like it is. ( it's ok) or alter the pipework snd fit an air separator.( air jec etc) before the pump.

It will expend up the cold feed and the new boiler will have a safety overheat, so no danger.

I was concerned about pumping over the head (maybe that's why the expansion pipe was disconnected in the first place!) but the feed is only 15mm - is that safe enough? The present setup has the feed tank about 8 feet above the boiler but I'm moving it right up into the loft space as part of the upgrade. The boiler is not new though - it's an old-school floor standing 'conventional' oil boiler. There is an overheat protection on it mind you. Don't have any experience or air separators - will investigate - thanks.

 

[stevetheplumber]

definitley been capped to stop pump over you need to run the vent and cold feed in before the pump close to each other and then you leave the aav in plce and cap where the cold feed went in

 

[Roger Welton]

Probably was an old gravity HW loop at some time in the past, as has been said will having pumping over and rather than sort out correctly they've just disconnected.

I'd move the cold feed and expansion to before the pump, possibly using a air sep depending on how I was feeling.

 

[Best]

Nearly certain it was capped off to prevent it pumping up.
It isn't dangerous if you have a feed pipe still connected and also add a pressure relief valve at the oil boiler. 3bar valve.
You are by far better with a sealed system if the pipe work, valves & joints are all sound. The old oil boiler needs to be suitable for sealed system though.

 

[Plumpplumber]

Thanks everyone for your help. I think I'll play safe and reinstate an expansion pipe but connect it (and the fill pipe) in between the boiler and the pump to prevent pumping over the head. The header tank will also be moved a bit higher which might help a bit too because at present the tank is only about a foot higher than the top of the upstairs radiators - I suspect that was the initial problem that caused pumping over and someone tried to cure it by disconnecting the expansion pipe.

I've attached an amended diagram.

 

[Plumpplumber]

Nearly certain it was capped off to prevent it pumping up.
It isn't dangerous if you have a feed pipe still connected and also add a pressure relief valve at the oil boiler. 3bar valve.
You are by far better with a sealed system if the pipe work, valves & joints are all sound. The old oil boiler needs to be suitable for sealed system though.

It's an old system and the house has a pumped 'mains' supply from a tank in a shed outside so pressure isn't too great. Not sure if the boiler would be suitable - It's a 'Rhino'..............

 

[Roger Welton]

Thanks everyone for your help. I think I'll play safe and reinstate an expansion pipe but connect it (and the fill pipe) in between the boiler and the pump to prevent pumping over the head. The header tank will also be moved a bit higher which might help a bit too because at present the tank is only about a foot higher than the top of the upstairs radiators - I suspect that was the initial problem that caused pumping over and someone tried to cure it by disconnecting the expansion pipe.

I've attached an amended diagram.

F+E teed in backwards

 

[Chalked]

.

Thanks everyone for your help. I think I'll play safe and reinstate an expansion pipe but connect it (and the fill pipe) in between the boiler and the pump to prevent pumping over the head. The header tank will also be moved a bit higher which might help a bit too because at present the tank is only about a foot higher than the top of the upstairs radiators - I suspect that was the initial problem that caused pumping over and someone tried to cure it by disconnecting the expansion pipe.

I've attached an amended diagram.

That's the way to do it.
You could also take the vent to the capped port in the boiler. If it's easy.
Or git an air separator. Like this.

 

[Best]

Thanks everyone for your help. I think I'll play safe and reinstate an expansion pipe but connect it (and the fill pipe) in between the boiler and the pump to prevent pumping over the head. The header tank will also be moved a bit higher which might help a bit too because at present the tank is only about a foot higher than the top of the upstairs radiators - I suspect that was the initial problem that caused pumping over and someone tried to cure it by disconnecting the expansion pipe.

I've attached an amended diagram.

No matter how much higher the f&e tank is raised, you still need any expansion pipe well above the tank. Raising the tank just really gives the system more pressure, but still allows the possibility of the vent pipe to pump over, unless it is piped as people have said.
To seal a system you can seal oil boilers to as little as 1/2 to 1bar pressure as it is more than enough pressure normally.

 

[Plumpplumber]

F+E teed in backwards

Thanks Roger - should the feed be next to the pump and the exp nearer the boiler?

 

[Plumpplumber]

No matter how much higher the f&e tank is raised, you still need any expansion pipe well above the tank. Raising the tank just really gives the system more pressure, but still allows the possibility of the vent pipe to pump over, unless it is piped as people have said.
To seal a system you can seal oil boilers to as little as 1/2 to 1bar pressure as it is more than enough pressure normally.

I was reckoning 450mm above water level - does that sound OK?

 

[Plumpplumber]

Yet another version of my diagram - swopped positions of feed and exp connections and indicated height of exp pipe into F&E. Not too confident about air separators so will keep that as a Plan B if required!

 

[Best]

I was reckoning 450mm above water level - does that sound OK?

Put it higher if you have the space. Remember if you are hitting the angled roof you can always then bend the pipe to that angle & run it up higher & back down to the tank. Keep the water level in the f&e tank to a minimum level of about 100mm max, - it is an expansion tank & only needs to be a top up tank with room for expansion, not a storage tank

 

[Plumpplumber]

Put it higher if you have the space. Remember if you are hitting the angled roof you can always then bend the pipe to that angle & run it up higher & back down to the tank. Keep the water level in the f&e tank to a minimum level of about 100mm max, - it is an expansion tank & only needs to be a top up tank with room for expansion, not a storage tank

Will do! Space is VERY tight in the loft but will keep water level at minimum and run the exp pipe right into the peak before dropping down.