Central heating system fault

[Roblincs]

Good morning, my central heating vent pipe is overflowing into the central heating header tank so I must have done something wrong.
I fitted my central heating system myself over 35 years ago as a Parkray gt111 solid fuel boiler system. In 1994 I converted it to gas with new pump and midway valve, and the makeup and vent pipes went where they were shown to go.
Last year I noticed that the water in the CH makeup tank was getting hot with the pump on the lowest speed so I moved the tank into the loft space to give more head, but the vent pipe still overflows, is anyone able to advise me what I've done wrong.
I might note that the hot water system is working fine with the HW makeup tank keeping to ambient temp.

 

[bernardgreen]

Possibly the pipe work is silting up. Thus the water from the pump cannot flow through the pipe work so the pressure from the pump is lifting water up the vent instead of driving it round the radiator circuit

 

[Roblincs]

The system that I have is a front and back design instead of up and down, and the front system seems to be a bit down on temperature, so I'll check that out. Thanks for the input,

 

[Roblincs]

I remember that I had the system power flushed after the floods of 2013 and although it wouldn't have shifted the lime scale it did give a fair flow. The pump is only 30cm away from the mid way valve, what would happen if I reversed the pump? Thanks

 

[picasso]

Blocked cold feed most likely.

 

[Roblincs]

Ah! I had an idea and put a magnet to the 22mm pipe that feeds the radiators and low and behold the copper pipe was magnetic, so the pipe is obviously blocked. So my question is; is there a water treatment that will dissolve rust stuck to the walls of the copper pipes. Many thanks, Bob.

 

[dilalio]

Better to cut out and replace the blocked area of pipe and even better to combine the feed and vent pipe while you’re at it.