Vent pipe discharging hot to F&E tank

[desmo]

I have a conventional, old fashioned indirect system.Feed/exp and cold storage tanks in loft. Cylinder in bathroom below. Over thesummer, as usual, I've been set to "hot water only". The HW used tobe gravity (22mm pipes to/from boiler) but a few years ago a plumber fitted apump on the return from the cylinder. On "water only" the upstairsrads get warm; at present only got one open. No recent mods to system, all'sbeen well for a long time, but in recent weeks the heating vent (not domesticwater vent) has been discharging a steady trickle of HOT water to the feed/exptank. This in turn fills the tank to the overflow. If I empty the tank, fillsup again when boiler is running. Ball cock to exp tank is OK. Boiler temp seton the low side, HW pump set to "1". Why is this happening, and whereis the "extra water" coming from? Only happens when the boiler &pump are running, so presume cylinder coil OK? Thanks, David.

 

[armyash]

Only had this once and it was a matter of adjusting the pump speed. Interested to see what the experts say.

 

[Best]

I would check the feed pipe from the exp/feed tank incase it is blocked somewhere.
Someone fitting a pump onto the gravity pipes without sorting out the feed & vent arrangement, was mad.
If your system is oil or gas, it may be possible to convert it to a sealed heating system if it is in decent order & all possible water loss points, - like leaky valves are fixed/replaced. By far the best system.