Open vented system flowing hot water into expansion tank

[bobby_la_mesma]

Dear Team

I would be grateful for some advice. I have just moved into a new house and I have heating problems. The previous tenants did not mention this.

I have an open vented central heating system. Y plan. The Vent pipe is constantly running hot water into the expansion tank, even with the pump set to 1 or 3. The three way valve operates on each port as I can feel hot water flowing on each side

The radiators do not get very warm and three do not get any heat at all unless you turn the hot water system off completely.
No radiator get hot at the bottom

I have been in the loft and the vent pipe cuts into the flow pipe with a 22mm pipe approx 1.5m below the expansion tank. The 15mm fill pipe cuts into the flow pipe in the airing cupboard approx 1.5m below where the vent pipe intersects and above the pump by 20cm. I have read that this may be the cause but I am look for some guidance before I start trying to re-locate pipes.

The pump is a British Gas Grundfos Pump, type Multihead G.

There are vents all over the system which have been bleed. all radiators have been bleed. The colour of the water in the system is not crystal clear but not full of sludge

Should I re-locate pipes or try a power flush or something else.

Thanks to all that reply

 

[45yearsagasman]

The cold feed and open vent must be connected into the system in the same place, on the flow pipe from the boiler just before the pump. The order being:- boiler, vent, cold feed, pump. Use an air separator instead of making the connections with tees. If you use tees then the max distance between the two connections must be less than 150mm. Using an air sep is the easiest.