I have an open vented central heating system fitted with a three way valve and a Grundfos Selectric pump. System has worked well for years. Recently there has been continuous flow of warm water to the expansion tank through the vent pipe. This only happens when the system calls for heating of water in the cylinder and not when calling for central heating only. What's changed and how do I fix this?
Overflowing vented central heating system
- Thread starter Foxchapel
- Start date
Sponsored Links
Has any work been done on the system recently?
No maintenance or any other work done for several years.
That probably explains why you have a problem.
Do you get the problem when its hot water only, or do you get it when the valve is in mid-position, i.e heating the rads and hot water at the same time?
Sponsored Links
Thanks for getting back to me.
The problem only occurs when it's asking the system to heat water. Overflow through the vent pipe occurs when heating water on its own and if heating water and heating the rads. There is no overflow if heating rads only. hope this is clear.
The problem only occurs when it's asking the system to heat water. Overflow through the vent pipe occurs when heating water on its own and if heating water and heating the rads. There is no overflow if heating rads only. hope this is clear.
Sounds like something blocked on the feed to the cylinder.
Do you still get hot water?
HW called for, valve opens and pump runs, can't make its way through the cylinder coil as normal so it forced up the vent pipe as path of least resistance, comes back down through the expansion tank feed.
I'd check the pipework that feeds the coil in the hot water cylinder with a magnet.
Sounds like it needs a service anyway to make sure the system isn't sludging itself up (which it has started to by the sounds of it!)
Do you still get hot water?
HW called for, valve opens and pump runs, can't make its way through the cylinder coil as normal so it forced up the vent pipe as path of least resistance, comes back down through the expansion tank feed.
I'd check the pipework that feeds the coil in the hot water cylinder with a magnet.
Sounds like it needs a service anyway to make sure the system isn't sludging itself up (which it has started to by the sounds of it!)
Scale deposits have partially blocked the cold feed/open vent pipe connections to the heating/HW circuit.
This causes a pressure imbalance which encourages water to travel up the open vent.
The other options are:
- Blocked primary coil in the cylinder.
- pump speed
Turning the pump speed down can help, but a paid visit is on the cards. NB: Left like this, your system will soon eat itself.
This causes a pressure imbalance which encourages water to travel up the open vent.
The other options are:
- Blocked primary coil in the cylinder.
- pump speed
Turning the pump speed down can help, but a paid visit is on the cards. NB: Left like this, your system will soon eat itself.
Just to add to the other replies, even a badly configured system can chug along with the faults going unnoticed for years, until eventually things start going awry, with a sequence something like:-
A small amount of water gets blown out the vent when the pump starts.
Water flowing up the vent gets aerated.
That air carries oxygen into the system.
The oxygen causes more corrosion.
The corrosion creates more sludge.
More sludge causes more blockages.
More blockages leads to more water pumping over,
etc.
etc.
A small amount of water gets blown out the vent when the pump starts.
Water flowing up the vent gets aerated.
That air carries oxygen into the system.
The oxygen causes more corrosion.
The corrosion creates more sludge.
More sludge causes more blockages.
More blockages leads to more water pumping over,
etc.
etc.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
