new motorised valve, look warm water & rads

[paul8745]

I have replaced the mid pos 3way valve on an open vented system (hot water would not heat without heating rads)& this partialy cured the problem but now water & rads only warm.
When i replaced the valve i tried to do it without draining,just closing all wheel head valves to isolate, but one must have been passng water so had to drain.
But the system does'nt make sense to me. There is a pipe & wheelhead valve connecting the flow from behind the 3 port valve to the return, this would seem to by pass the cylendr & rads to some extent. I think this valve was only partialy open before I started but I dont know how much.
Help what is the purpose of this pipe & should the valve be closed?

 

[Plumbstar Tom]

this is your bypass valve

Needs to be left cracked open slightly to stop the pump from pumping against a dead end

 

[paul8745]

Many thanks Tom.

 

[Puddle]

Fitting a auto by pass would be better,this stays closed until needed,also make sure you have a gate valve on cylinder return so you can balance down
Both above will help to provide a good flow through the heating side of the system

imho

 

[paul8745]

Hi folks .
Thanks for your answer to my problem the other day; I wonder if I could trouble you for further advice?
I am having trouble getting the right flow through the system.
I followed Toms advice, turned off the bypass valve then cracked it open just a little (about 1 -1 1/2 turns until the pipe started to get warm).
This improved things but the water was still not as hot as before & rads not as hot so I turned down the return valve from the cylinder to try to balance it, back to stage 1, look warm water & rads.
How do I set this up from scratch as I am still having problems.?
The only things I have touched are the wheel head valves & the mid pos valve so the boiler, cylinder & room stats are unchanged
Thanks very much
Paul