Gas Central Heating question

[p]

I have a question about my gas central heating system. I have an open vented, pumped flow, wet system. I have bled all the rads on the system. I have three rads which are probably the furthest from the pump (one of which is in my cellar) that have cold spots.

I had to turn the pump down last year because it was causing water to vent to the outside of the house.

If I turn the pump up will this warm up the rads?

Do I need to turn the thermostats up allow the system to heat to a higher temperature, and so heat up these rads?

If I do have to turn up the pump pressure is there any other way of stopping the water venting to the outside?

Thanking you in advance.

[Set Square]

What do you mean by "cold spots"? Is part of the radiator hot, and part cold? If so, which part is cold?

If the centre bottom section is cold, it suggests that it's full of sludge - and needs to be disconnected and taken outside and flushed thoroughly with a hose.

If you have radiators which are not getting hot at all - or are uniformly warm but cooler than the others, it suggests that the system needs to be balanced by turning down the lockshield valves on the hottest rads. This, in, turn, may require an increase in pump speed to get sufficient flow round the whole system.

What exactly do you mean about causing water to vent to the outside of the house? Are you saying that the water in the F&E tank was above the overflow level? Maybe it was too high to start with, with the system cold. When cold, there should only be about 2 or 3 inches of water in the bottom of the tank - leaving lots of room for expansion. I still don't quite understand why the pump would make it overflow, though. Was there a continuous flow of water out of the vent pipe back into the tank (known as "pumping over")? If so, the positions where the fill and vent pipes connect into the main pipework may need to be adjusted.

[p]

Cold spot is toward the middle of the rad.

Which valve is the lockshield valve?

I will have to check back on that one.

Many thanks

[Set Square]

Sounds like sludge then. Action as per my previous post.

Each rad should have 2 valves. One has a knob which you can rotate by hand to turn the radiator on and off. The other one has just a shaft with flats or a square end - possibly under a non-rotating cover - and needs a spanner to operate it. This is the lockshield valve, and has to be adjusted to balance the system.

[Ed Sirett]

This problem needs to fixed before anything else is done. If the F&E tank is overflowing then it implies that air is being drawn into the system when the pump is on a higher speed. This is because the layout of the pipework is wrong and specifically the pump is before the point where the water from the feed tank joins the main circuit.

When that problem is fixed then ten you can move on to curing the consequential damaged (possible sludge in the some radiators). Finally you can then address why some rads are colder than others.