Why move the FE tank feed to other side of pump/valve?

[gcjl]

I've recently noticed that our FE tank is overflowing because when the CH is on there is a steady stream of hot water filling up the FE tank and going out the overflow. I think this may have been doing this for some time.
The ball valve seems ok.

After reading lots of other posts on this I believe the vent and feed to the FE tank should be quite close together and before the pump and Y valve.
It seems that my system has been modified such that the original FE feed from before the pump has been capped off and it is now feeding into the hot water side, after the valve, but before entering the HW tank.
The FE vent is still on the boiler side of the pump.

Does anyone know why this modification might have been done - is it a recognised cure for something?
I'm not sure if it related to the overflowing problem, but it would be nice to know why it was done.

We've been in the house 2 years.
I know that the boiler was replaced just before we bought the house, and the only othe mod that I can see is that 2 power shower have been added into the system some time ago.

It's an open vented system.
FE tank and cold water tank in loft - on same level base (water in CW tank about 15cm higher than FE tank)
Ball valves seem ok.
Condensing gas boiler (sorry don't have model at mo)
Honeywell Y valve.

 

[JamesTheakston]

how much gap is there between the water level in the F & R tank (when htg and hw OFF) and the overflow pipe level?

 

[gcjl]

At the moment, it's small, maybe 1 inch - I know there shouldn't be much water in the tank, but the vent keeps filling the tank.
It's more than just expansion of water coming from the vent, it's a continual stream when the CH is on.
I could take water out of the tank, but I'm sure it would fill up again after some time.

 

[JamesTheakston]

water shouldn't come from the vent on expanding anyway, but up from the cold feed.

how far is your pump from the F & E?

 

[gcjl]

Pump and valve, right next to HW tank in airing cupboard in bathroom (first floor), F&E tank in loft above ~ 10ft away.
Boiler in garage below on ground floor.

 

[JamesTheakston]

Is the water coming out of the vent pipe or back up the cold feed? i'd say your water level is way to high anyway in the f & e cistern. how high is your vent pipe between the water level and from where it bends over into a u shape?

 

[gcjl]

It's definitely coming from the vent pipe. (It's more than just a drip, it's like a tap on a low setting, if you know what I mean).
It doesn't happen when CH is off.
I'm not at home at the moment to give you an accurate measurement, but I'd estimate the top of the vent is 15 to 20 cm above the water level.

 

[JamesTheakston]

That is not enough, the vent pipe must rise above the water level about 450mm minimum before looping over (I think you are getting pumping over, as it is only when your htg is on).

This has been like this since first installed I take it? Or have you had a new pump installed anytime recently?

Measure the vent pipe distance when you get home.
And the reason why overflwoing is happening is because the water leel is set too high as well.

 

[seco services]

the whole lot sounds like a mess.

 

[gcjl]

I've not made any mods/adjustments in the 2 years we've been in the house.
I'll reduce the water level and measure the gap accurately and report back.

Thanks for your help so far.

BTW, does the moving of the feed position to after the pump/value that I mentioned in the OP mean anything to you?
I would have thought that the way it is now, when the CH only is on the feed from the F&E tank is isolated?

 

[JamesTheakston]

The feed after the pump could mean water being pumped up it (as under positie pressure) but your probelm is with the vent pumping over.

Unless both are?