Heating overflowing from vent

[Morrispd]

Hi, I'm after some help regarding my Father in laws heating system.
He has had a local engineer around but hasn't had a fix and is very remote so I'm looking at the issue before arranging someone to try to fix. He is on oil and has a modern raeburn boiler/range. He has a vented system with wented hot water tank, s plan wiring and the CH vent pipe goes out of the roof possible 1m above the highest rad (rooms in roof). When the CH is on he is losing water out of the vent pipe and has to bleed the highest radiator daily. I'm assuming this is expansion causing the overflow but why hasn't this always happened? He is obviously diluting any inhibitor daily and wasting a lot of water, where is the problem likely to be? If you need any more info about the system please let me know, I'm an engineer and quite handy. I just can't get my head around what the fault may be and as nothing has changed I can't see how there is an inherent problem with the install. TIA for any insight.

 

[ShaunCorbs]

Anything been changed ?

 

[Morrispd]

Anything been changed ?

I don't think so

 

[exedon2]

Some clear pictures of pump motorised valves and how open vent/cold feed is connected would be useful or a sketch of pipework layout?
Which model Rayburn? from memory on the central heating cookers Rayburn ask for a close coupled open vent/cold feed (max 150mm between)
You can also run then as a sealed system the prv needs to be 2 bar.

 

[John.g]

As above, photo handy, if the system has a control stat and a overetemp stat then can be converted to a combined cold feed and vent like my 50 year old system which will never pump over or draw any air in.

 

[Morrispd]

Some clear pictures of pump motorised valves and how open vent/cold feed is connected would be useful or a sketch of pipework layout?
Which model Rayburn? from memory on the central heating cookers Rayburn ask for a close coupled open vent/cold feed (max 150mm between)
You can also run then as a sealed system the prv needs to be 2 bar.

 

[Morrispd]

There is the stat on the raeburn and on the cylinder. Cold feed is to the 2 tanks, CH and DHW tanks. Dribbling from the vent in the roof is only when the central heating is on and is greatly reduced if the ch temp Is reduced on the boiler

 

[Morrispd]

As above, photo handy, if the system has a control stat and a overetemp stat then can be converted to a combined cold feed and vent like my 50 year old system which will never pump over or draw any air in.

I don't know why it hasn't always been like this as nothing has changed so am tring to identify a fault that may not be there, what is involved with combined feed and vent?

 

[exedon2]

On that model of Rayburn if open vented the manufacturers instructions ask for a 22mm open vent and a 22mm cold feed in a close coupled arrangement.
You can also use sealed system that model is ok with standard 3 bar prv.
System should have had system auto bypass fitted as there is overheat stat that runs the pump .

 

[Morrispd]

How do I identify this
"System should have had system auto bypass fitted as there is overheat stat that runs the pump"
Pump does seem to run unnecessarily but current setup has been in 12 years without requiring excessive bleeding and without losing water from the vent.