central heating puzzler

[jontheplum]

mother in laws rads are playing up 2 sometimes work upstairs two sometimes downstairs pump seems to be working drained system refilled adding sludge remover left for 10 days drained flushed refilled adding inhibitor .two strange things happened after venting of rads i run boiler for 10 minutes then vented rads again but upstairs rads were drawing air in and the f'n'e tank was spilling out the over flow.had set the fov to a low level and water had'nt really got hot enough to warrant major exspansion, i jugged some water out and the level didnt rise anymore.when i drained down previously i shut off supply to cold water storage tank to check for a split coil but the level of water didnt drop ........vented dhw,open vent heating ,old looking floorstanding potterton......??????????????????????????

 

[Slugbabydotcom]

As your system fills with air the displaced water appears in the f & e tank.
Problem could be helped by turning your pump to a lower speed.

If that doesn't work then there is a good possibility that system blockages and or bad system design are at the root of your problem. The part of the system that is likely to be blocked is the feed pipe where it connects to the system. This is because the water there is fairly stagnant compared to the rest of the system where the water moves constantly.

A system where the pump lies in between the feed and vent or even too close to either of these pipes can cause ingress of air and pumping over as you describe.

 

[jontheplum]

pump is inside boiler casing so would presume its in a recomended location dhw cylinder is smack bang next to boiler ,wether this would make any difference i dont know . would pumping over cause the water to go back up the feed pipe [ i thought it was when it went through vent which isnt happening].....p.s thanks for reply.