URGENT water level changes significantly in expansion pipe (open vented system)

[Bruce43]

I have made some adaptations to the layout of an existing open vented one pipe system. The pump is now some 6 or 7 metres away from the boiler. The cold feed is on the negative side of the pump as is the expansion pipe. The order of fixing is expansion pipe - cold feed - pump. When the pump stops around 400 ccs of water is dropped into the header tank. Is it normal for oscillations to occur in the expansion pipe on pump starting and stopping?

 

[doitmyself]

1. Do the cold feed and vent connect to the flow from boiler to pump within six inches of each other?

2, Is the top of the bend in the vent pipe at least 450mm above the tank's water level when hot?

 

[Chalked]

If it’s dumping water when going off. It will be doing the opposite, when turning on, ( sucking) this will introduce air in the system. The vat and feed should be connected into the pipework correctly, to stop this.
there are a few ways of achieving this. But depends on you pipe layout

 

[centralheatking]

I have made some adaptations to the layout of an existing open vented one pipe system. The pump is now some 6 or 7 metres away from the boiler. The cold feed is on the negative side of the pump as is the expansion pipe. The order of fixing is expansion pipe - cold feed - pump. When the pump stops around 400 ccs of water is dropped into the header tank. Is it normal for oscillations to occur in the expansion pipe on pump starting and stopping?

Ok Bruce I think I get what you have done but put up a diagram of your system complete with your 'adaptions' please then we can all help you quick time
centralheatking

 

[Bruce43]

Ok Bruce I think I get what you have done but put up a diagram of your system complete with your 'adaptions' please then we can all help you quick time
centralheatking

I think the problem is rebound from the motorized valves opening and shutting. They are within 2 metres of the expansion pipe. Order of fitting on flow piping is: expansion - cold feed (within 6ins)-pump-motorized valves. I know nothing about motorized valves. The ones fitted are Honeywell (spring action). Is it possible to get valves that operate at a much slower speed (ball valves??) ? Slowing the operation down should cure the problem. Thanks.
[automerge]1575649952[/automerge]

1. Do the cold feed and vent connect to the flow from boiler to pump within six inches of each other?

2, Is the top of the bend in the vent pipe at least 450mm above the tank's water level when hot?

Thanks for this, but I think the problem is due to the motorized control valves operating quickly. They are within 2 metres of the expansion pipe. Is it possible to buy slow action valves?
[automerge]1575650190[/automerge]

If it’s dumping water when going off. It will be doing the opposite, when turning on, ( sucking) this will introduce air in the system. The vat and feed should be connected into the pipework correctly, to stop this.
there are a few ways of achieving this. But depends on you pipe layout

If it’s dumping water when going off. It will be doing the opposite, when turning on, ( sucking) this will introduce air in the system. The vat and feed should be connected into the pipework correctly, to stop this.
there are a few ways of achieving this. But depends on you pipe layout

Thanks for your reply. I think the problem is speed of operation of motorized valves which are within 2 metres. Is it possible to buy slow operating motorized valves - this should solve the problem.

 

[John.g]

My Honeywell valves are relatively slow in operation, 6 to 10 seconds in either direction. If you have a gas fired boiler then you may have pump overrun....the pump continues to run on for ~ 2 minutes so the water has to go somewhere, normally a Automatic bypass valve fitted between the flow and return, the ABV setting may be too high, sometimes the ABV is part of the boiler internal plumbing in which case you can't do anything about it. if a oil fired boiler then unlikely that a pump overrun is fitted. You might get someone to switch off both zones and watch/see if the pump runs on and for how long,

 

[Bruce43]

My Honeywell valves are relatively slow in operation, 6 to 10 seconds in either direction. If you have a gas fired boiler then you may have pump overrun....the pump continues to run on for ~ 2 minutes so the water has to go somewhere, normally a Automatic bypass valve fitted between the flow and return, the ABV setting may be too high, sometimes the ABV is part of the boiler internal plumbing in which case you can't do anything about it. if a oil fired boiler then unlikely that a pump overrun is fitted. You might get someone to switch off both zones and watch/see if the pump runs on and for how long,

Thanks I'll try that.