Overflow running when heating or hot water on

[Grahamrae]

Hi all, I have a customer with open vented system,cold feed from f&e tank is teed into flow just above cylinder coil where in enters attic as expansion/vent which terminates through roof
The tank overflows whenever heating or hot water is on and stops as soon as boiler/pump goes off,so it’s definitely filling tank through feed pipe
A new boiler,3 port valve have recently been fitted but this ongoing problem is still occurring
I thought coil maybe had pinhole but surely this would cause overflow to continually run as water tried to self level against cwst for cylinder
I’m at a loss how it’s happening only when boiler and pump on wether heating or hot water on
Any pointers or advice greatly appreciated

 

[Ben-gee]

Which tank is overflowing?
What are relative heights of CWST and F&E ?

 

[Grahamrae]

Which tank is overflowing?
What are relative heights of CWST and F&E ?

F&e is overflowing when boiler on for hot water or heating
Cwst slightly higher than f&e tank
As soon as boiler cuts off overflow stops

 

[SJB060685]

How is the vent, cold fill and pump positioned? Vent and cold fill should be before the pump

 

[Grahamrae]

How is the vent, cold fill and pump positioned? Vent and cold fill should be before the pump

Vent from flow on cylinder coil,cold feed same place
Pump on return just before boiler

 

[king of pipes]

Any pictures ??? Please

 

[Grahamrae]

Any pictures ??? Please

Here’s a quick drawing of layout

 

[SJB060685]

If that is genuinely how its piped up then that is dangerous.
Is that a diverter or mid position valve? Not that that makes any difference.
As it is the combined vent and cold feed are only able to function when in HW mode, if there was an overheating problem when in CH mode only then there's nowhere for the water to vent. Also when in HW mode the pump is most likely venting over, im assuming you're seeing it overflow down and off the roof?
If what ive said above is correct this needs to be redone ASAP and there a several ways to go about it, the best way will be to reposition vent and cold fill before the pump on the flow before three port.

 

[Grahamrae]

If that is genuinely how its piped up then that is dangerous.
Is that a diverter or mid position valve? Not that that makes any difference.
As it is the combined vent and cold feed are only able to function when in HW mode, if there was an overheating problem when in CH mode only then there's nowhere for the water to vent. Also when in HW mode the pump is most likely venting over, im assuming you're seeing it overflow down and off the roof?
If what ive said above is correct this needs to be redone ASAP and there a several ways to go about it, the best way will be to reposition vent and cold fill before the pump on the flow before three port.

No it’s overflowing through the overflow pipe
It’s a mid position valve
Would you recommend changing pump onto flow or would changing cold feed and vent be enough
Thanks

 

[SJB060685]

First off I would reposition pump to the primary flow 150mm after the tee for vent and cold fill. This will make it safe and should prevent the problem you're experiencing. Also at the moment the majority of the system is under negative pressure so you could be drawing in air and have sludge/corrosion problems

 

[John.g]

No it’s overflowing through the overflow pipe
It’s a mid position valve
Would you recommend changing pump onto flow or would changing cold feed and vent be enough
Thanks

You say that its returning through the cold fill even on CH, if so, and if the 3 port valve is installed&working correctly then from your sketch it would seem that the only way this can happen is that the water flows through the rads and then up the return at the T just before the pump suction, then through the cylinder coil and back into the F&E tank which seems highly improbable.
[automerge]1593979747[/automerge]
My 48 year old system is very like that with combined vent & cold feed except that I have 2 port valves, I run my circ pump with a 3M head.

 

[king of pipes]

Piped wrong bud it should be like this . Kop

 

[SJB060685]

The above is for a Y plan when he has a W plan, not that it makes any difference. As I said there's several ways to repipe in this situation but the most common way is V,C,P on the flow, that is vent then cold fill within 150mm of each other, creating the neutral point of the system and then the pump shortly after. This will prevent any pumping over, while leaving the vent uncompromised for safety purposes and will also provide a positive pressure throughout the system.

 

[John.g]

Correct but I feel there is still some other fundamental problem there as that system on HW only should IMO work perfectly OK with no pump back.

 

[SJB060685]

I agree, something doesn't quite add up. With its current position the head of water in header tank should not pump over, all the system will be doing is circulating under a negative pressure
[automerge]1593986763[/automerge]
Its quite possible the system is sludged up due to the negative pressure the majority of the system is under in operation causing blockages enough to create a path of resistance and vent over
[automerge]1593991160[/automerge]
Edit : Not that, something doesn't add up

 

[king of pipes]

Piped wrong bud it should be like this . Kop

The above is for a Y plan when he has a W plan, not that it makes any difference. As I said there's several ways to repipe in this situation but the most common way is V,C,P on the flow, that is vent then cold fill within 150mm of each other, creating the neutral point of the system and then the pump shortly after. This will prevent any pumping over, while leaving the vent uncompromised for safety purposes and will also provide a positive pressure throughout the system.

as you say not much difference

 

[RSD]

No it’s overflowing through the overflow pipe
It’s a mid position valve
Would you recommend changing pump onto flow or would changing cold feed and vent be enough
Thanks

Possible sludge build up/blockage - I would have had the F&E tee'd into the coil return, rather than the flow?

 

[John.g]

The vent and cold feed are combined so as that there is no imbalance between them which prevents pump over through the vent or pump back through the cold feed, this seems very strange as water must be pumping back into the F&E tank to create that overflow but what is replacing it as the ballcock will be shut?. It would seem unlikely that there is a blockage as the water seems to be flowing freely back up through the combined F&E.
Maybe Grahamrae has found the solution.

 

[RSD]

The vent and cold feed are combined so as that there is no imbalance between them which prevents pump over through the vent or pump back through the cold feed, this seems very strange as water must be pumping back into the F&E tank to create that overflow but what is replacing it as the ballcock will be shut?. It would seem unlikely that there is a blockage as the water seems to be flowing freely back up through the combined F&E.
Maybe Grahamrae has found the solution.

It shouldn't be going up the vent, but only up the cold feed (due to expansion of the heated water). There could be sludge build up/blockage at the tee on the coil flow, or wherever its tee'd into the Vent?
Wonder what is the pump setting on - should only be on 1/lowest speed?

 

[John.g]

"No it’s overflowing through the overflow pipe" post #13 and not the vent?.