Plumbing Help!

[Beeezer]

This is a picture of the heating plumbing on vessel.
It’s been a pig of a system over the years, sometimes it bleeds really easy, sometimes it takes ages.
The other week a twelve year old pump packed up.
Put a new pump on this weekend and I’m biggered if I can get the air out of the system.
This pic is basically how it looks, there’s another rad in there.
Is there a better way this system could be done, bearing in mind the plastic pipes rum behind fixed beds, water tanks and cupboards
Thanks, I know bigger all about heating and plumbing.

 

[Dozzer]

Unless im reading that wrong your are pumping the returning cold water into the top of the back boiler?
Would expect flow to be from hot side towards rads and have return leg on cold side/lower

 

[Kayos]

Pump on return with cold feed and vent behind it, so the pump is pulling on the cold feed. We learned it as VIP Vent, Inlet, Pump

 

[voipio]

Is the topography more or less as shown in the diagram i.e. header tank is highest, back boiler's inlet is higher than the outlet? Where are the existing bleed vents? There should be a vent at the highest part of the inlet to the boiler, or on the boiler itself, another one at the top of the radiator, and another close to the header tank. The return that passes close to the header tank would benefit from having a "blind" vertical tee about 150-200mm tall, ideally from 19mm pipe, with a vent at the top end (it could be an automatic vent). The thinking behind having the tee is that gas bubbles (air or hydrogen) passing the tee, would tend to drift upwards and be captured in the tee.

 

[Beeezer]

Unless im reading that wrong your are pumping the returning cold water into the top of the back boiler?
Would expect flow to be from hot side towards rads and have return leg on cold side/lower

I was thinking the same.

 

[Beeezer]

Is the topography more or less as shown in the diagram i.e. header tank is highest, back boiler's inlet is higher than the outlet? Where are the existing bleed vents? There should be a vent at the highest part of the inlet to the boiler, or on the boiler itself, another one at the top of the radiator, and another close to the header tank. The return that passes close to the header tank would benefit from having a "blind" vertical tee about 150-200mm tall, ideally from 19mm pipe, with a vent at the top end (it could be an automatic vent). The thinking behind having the tee is that gas bubbles (air or hydrogen) passing the tee, would tend to drift upwards and be captured in the tee.

The header tank is higher than shown in the scribble, there’s a bleed valve on top of the back boiler and bleed valves on the rads.

 

[Beeezer]

So it should help me if I turn the pump round so the flow is going the other way??

 

[voipio]

It should be fine as it is. Try running the pump for a short while, then stop the pump, and bleed each vent. Repeat a couple more times, until little or no air comes out when bleeding. Make sure that the header tank water level is above the level of any of the bleed valves. Is the header tank vented to atmosphere? The diagram makes it look like it's a closed vessel.

Since yours is likely not to be a pressurised system, the internal static pressures will be low. There's a good chance that, when the pump is running, parts of the system will be below atmospheric pressure, so opening bleed vents will tend to draw air in to the system.

 

[voipio]

There would be some advantage in having the pump located in the leg going to the back boiler. As it stands, based on the drawing, the flow from the pump passes into the right hand side of the rad, then out of the rad, back to the header tank loop. The water path to the boiler doesn't get to see the full pump output, since the radiator is creating a shunt.

 

[dobbslc]

Have you tried turning all the rad valves off?
That would force any air around the system and hopefully up the vent pipe to the header tank.

 

[Beeezer]

Have you tried turning all the rad valves off?
That would force any air around the system and hopefully up the vent pipe to the header tank.

I did try that yesterday.
I’ve given up with it now until next weekend.

 

[Beeezer]

There would be some advantage in having the pump located in the leg going to the back boiler. As it stands, based on the drawing, the flow from the pump passes into the right hand side of the rad, then out of the rad, back to the header tank loop. The water path to the boiler doesn't get to see the full pump output, since the radiator is creating a shunt.

Thanks, could you put a mark on my pic as to where you recon please.

 

[Blobber]

The feed from the header tank isn't blocked or restricted at the "T" joint? Used to be a common problem
I've had systems before where I've had to fill them from a hose connected to a drain cock near a rad

 

[gaz1]

kayos is right by the way if you fit the pump on the feed you burn out the pumps faster the return side is the colder side

from your pic you would get feed through the rad if its designed and plumbed in that way so it wouldnt be effective on pumping hot water from the back boiler fit the pump on the other side of the return pipe of the rad

heat travels the shortest way possible the same is with the pump it would back flow taking the shortest path back to the pump again even with reduced flow on the rad itself

 

[voipio]

Thanks, could you put a mark on my pic as to where you recon please.

The red X marks show the two possible suggested pump positions.
For slightly cooler water to pass through the pump, set the flow direction towards the boiler.

 

[Beeezer]

The red X marks show the two possible suggested pump positions.
For slightly cooler water to pass through the pump, set the flow direction towards the boiler.
View attachment 531097

Thanks, so flow into the bottom of the back boiler.

 

[brightspark]

Thanks, so flow into the bottom of the back boiler.

it makes sence to have it in the return to the boiler heat rises and forces the cold water down

 

[gaz1]

Thanks, so flow into the bottom of the back boiler.

no return is usually bottom connection

check your boilers diagrams for flow and return connections

gravity fed is definatly bottom connection