Trying to understand my CH system

[gtxzag]

Hi all,

I'm trying to fault find on my CH system. As far as I can work out it is an open vent fully pumped system. The hot water tank is a double input Hercal boiler. On one side of the boiler, the side that has the three position motorized valve there is an output pipe quite low down the tank. This output pipe has a single valve/stop cock, what does this do?

After draining and refilling the system at the beginning of the week I had no heat to the radiators until I moved the valve fully to the right. Once the radiators were warming up I thought this was correct so left it as it was. This resulted in no hot water. Turning the wheel to the left this seemed to give both heating and hot water.

Having to drain again today, due to adding a clearing additive last time, I can get all but one radiator to heat up, but I need to move this valve to kick everything into operation.

Sorry about the length of this,
What does the valve do?
What position should it be in?
What can I do about this cold radiator?

View media item 42671
Thanks in advance

GTXZAG

 

[twgas]

If that diagram is a true representation of your set-up you problem will be sludge building up in the system pipework and radiators. The pump should be between the H and the three port valve.
the valve at the bottom will be to balnce the system, it should be set somewhere between full on and full off.

 

[ChrisR]

It shouldn't make any diffreence to the CH when you're on CH only, though 3 way valves can "let by".
With the system cold, put the CH only on. That valve shouldn't get warm.

I normally set them one full turn opened from shut, after the play.

Your cold rad
try
1) close all the other rads, pit CH only on, and it should get hot. That might cure it.
Then balance the system ( look it up!)

2) If it won't go, shut its valves, drain it and take it into the garden for a hosing through.

 

[gtxzag]

Thanks Mick,

Just checked and the diagram as accurate, is the pump in the wrong place?

I had used some cleaner to avoid the sludge build up. Would it be worth draining that radiator and seeing what happens. If I drain the 'dodgy' radiator I presume it will prove the sludge build up or hopefully remove it.

I take it you balance the system by just finding the best position for the valve.

Gary

 

[twgas]

as already said, the pump should be between cold feed and motorised valve