Valve between flow and return just after pump (open vented system)

[Mondrota]

Hi, I'm new to this forum so please bear with me.
I recently bought a house and have an old open vented system installed. The problem with it is that the boiler keeps overheating and shutting down for a while to cool down. I think it's due to poor circulation. The pump seems ok so I suspect there might be a blockage somewhere. While I was diagnosing the installation, i noticed that there is a valve connecting hot water flow just after pump to the return as in attached picture. Can someone explain what is its purpose? Also any tips regarding overheating problem would be much appreciated.
Forgot to mention that the installation upstairs is 15mm and 2 rads downstairs use 8mm microbore.
All of the rads barely get hot-ish when the heating is on. The boiler thermostat is on max, and boiler makes a "kettle - ing" noise.
Thank you.

 

[Dotty]

Should be your automatic bypass valve.

Put very simply it provides a route for the pumped water to take in the event that the pump runs on after valves have automatically closed (zone valves and thermostatic rad valves).

You may need to seriously consider calling someone in, microbore is hell when it plays up, even for us!

 

[snowhead]

Pump seems OK?

Have you removed it and checked the impellor is intact and the housing is not blocked?

Or just removed the end cap and the shaft is spinning?

 

[Mondrota]

Removed the end cap and it is spinning. Also when I open the mentioned valve i can hear the water rushing through the pipes and somehow the rads get a bit warmer than when the valve is shut. I'm planning to have a combi boiler installed when the weather is warmer but I would love to have this sorted ASAP as it would save me replacement ing the whole installation later.
Regards

 

[lame plumber]

just because the pump is turn doesnt mean its working properly Im afraid to say. or you may have sludge in the system restricting flow, which would mean a combi wouldnt fair well unless you ensure the system is properly flushed thro before swapping boilers. combi plate hexes do nott like dirty systems! unless they are combis that do not use plate hexes ie ferrolli or intergas to name a couple, one of which is yet to be peoven reliable!

 

[Mondrota]

I forgot to mention that it gets really hot, hotter than the radiators lol. That would probably indicate that it's having trouble moving water? And the water flows rapidly when valve is open. That makes me think the pump should be ok. What do you reckon?

 

[lame plumber]

by opening the balancing valve you are allowing all the hot water to bypass the heating circuit and flow straight back to the boiler return! stop fiddling and get a proper heating engineer in.

 

[Mondrota]

That's what I thought, but surprisingly the rads get warmer when valve is open. This must be proper messed up.

 

[Mondrota]

This is what it looks like, to give you all a better picture.
Thank you for trying.

 

[snowhead]

Do you get plenty of hot water from the cylinder or does it run out quickly?

And the pump should be horizontal, but I bet the door won't shut if it is.

 

[heliotrope]

As your system appears to be Y plan the bypass valve is not strictly necessary.

Closing shut should give a better circulation around the heating. On such an old
system and with small bore pipework blocked pipes could not be ruled out.

Again, the pump may appear to be working ok but the impeller could be partly
blocked. You would need to isolate the pump at the valves and remove the head
to check.

 

[Mondrota]

There's plenty of hot water in the cylinder, this works ok - no overheating. Maybe the picture doesn't show it too well but the pump is horizontal.

 

[Mondrota]

Ok, thanks, I will consider taking the pump out and apart. Will update once complete, meanwhile keep the ideas flowing

 

[lame plumber]

and now I predict it starts to go wrong,beware the sheared gate valve, or if more cautious air locks galore

 

[Mondrota]

Just had it out and it doesn't look too bad to me. What do you think?

 

[petercj]

Kettling, boiler overheating, and cool radiators (particularly lower down) are common symptoms when a system is sludged up, which is not to rule out other issues that might be aggravating matters.

If you are having a new boiler fitted, then a powerflush is the way to go, so why not get it done sooner rather than later. Fitting a filter will also provide protection for the new boiler. If the powerflush doesn't resolve matters, then the engineer doing it can look into any additional problems.

 

[lame plumber]

looks like most of the broken and working ones I see! We arent there to be able to assess the overall picture Im afraid.