Two stone cold radiators

[notaplumber1967]

Ok. Get a cup of tea this is a long one! Where do I start? I have a small two bedroom house with 6 rads, 3 up and 3 down.
WHAT I HAVE GOT: It's a pumped system, I think some plumbers would call it an H plan, take a look at the pics and see if I am right. The F&E tank is at high level in the loft and the expansion pipe extends a good 12-14" above the tank. There are no TRV's fitted to the rads. The cylinder, pump and valve are in the 1st floor airing cupboard and the boiler is a back boiler on the ground floor almost directly below the cylinder.
THE PROBLEM: I have one rad upstairs that is cold and one rad downstairs that is cold and I get a constant flow of hot water in the F&E tank from the expansion pipe when I put the pump on full (pump over I believe?)
WHAT I HAVE DONE SO FAR:I have drained the system by using each drain cock (there is one on each ground floor rad). I made sure I got as much water out as possible by opening the bleed screws (upstairs first then downstairs.) I changed the pump for a new one. I put cleaner in and refilled but still no joy.

This was over a year ago. I have had two plumbers look at it since but they never come back (I give them cups of tea as well!) The last plumber changed the motorized valve and head. So I tried again but this time I took up some floor boards to get an idea of how it was plumbed. I found that the main flow and return run is in 22mm pipe but the section that is cold is in 15mm pipe. Is this wrong? (check my diagram). It's only a 3 or 4 meter run to the furthest radiator in that section, so I don't think it would be the problem. The house is small so nothing is very far from the pump! I also took the rad valves off to check them and they are all ok. I don't think there are any blockages in the rads or pipes because when it refills all the rads bleed well. I will say however that when I drained the system from the drain cock on the ground floor rad that won't work, it drained slowly. There is a drain cock at the back boiler as well but I didn't use that one (not sure if that's relevant).
As for the pump over problem I have not got a clue!

I wonder if the pump is in the wrong place (maybe it should be down near the boiler) or if the short cross over pipe (see pic) should be higher and further away from the pump. I have not taken up enough floor boards to get a full picture of the system, so the diagram is not for definite. How can I be absolutely sure that all the pipes and rads are not blocked? So what do you think, is the pump over and the cold rads part of the same problem? Is there a blockage? Could there be a leak in the heat exchanger taking some of the pump pressure away? (we don't get any brown water coming out of the taps).

Well here are the pics and the diagram I hope they shine a bit of light on it for you guys, because believe me, I am close to moving house to sort this one out! Thank you for reading.

 

[ChrisR]

Try Balancing - see reference section.

 

[notaplumber1967]

Try Balancing - see reference section.

Sorry I forgot to mention that I have tried that, even closed the valves on the other four rads but still no joy, but the pipes get warmer a little further on (about a 1 ft).

 

[MANDATE]

You say you don't think there's any blockage cause the rads bleed well.
The way I see it, if a blockage exists, it may not affect the bleeding.
Supposing the return pipe is blocked, water can still reach the radiator bleed valve coming up from the flow pipe.
I think you should bleed it first with only flow valve open and then with only the return valve open. If there's a blockage I would expect it to bleed easily one way and not the other. In fact you could go further and remove a radiator, then run off water first from one side then the other.
I once did this to remove an air lock. In fact I used 6ft of clear plastic hose with a tap connector on each end and with both ends connected and system running I could eventually observe the water flowing through the pipe and taking air bubbles along with it to the next radiator.
I think the way a system is filled from the feed pipe down to a 'Tee' the water is free to go both left and right. Air gets pushed into radiators but it's possible some gets trapped in pipe work between radiators.The pump can't deal with it because the air compresses and there's no escape route for the water.
Also don't forget to bleed the pump
Hope it helps a little, but I'm not a plumber

 

[notaplumber1967]

@ MANDATE
Thanks for that input. You have helped to make a things a little clearer regarding blockages.

 

[Softus]

Marvellously clear images and description!

Everything is screaming "blockage" here, but not just one I suspect.

First point: if you experience "pumping over", then, assuming that the pump is pumping downwards as you've indicated, then this implies there is less resistance to flow up through the vent than there is in the short horizontal section of 22mm pipework just above the pump. Even though my intution cries "surely not!", this is the logical conclusion.

Second point: if you have some hot rads and some cold, then you have one or more blockages. I would suspect (a) rad valves, and (b) any long sections of 15mm pipework - if there are any long horizontal runs then even more so.

Here's a question, before I forget it - what's all the white stuff lying on the pump? If it's only a year old then why so manked up already?

If I were there, I'd want to go for a partial drain down (with all rad valves shut) and then cut into the short horizontal pipe between the vent and cold feed pipes, to see what's in there. You can easily remake this pipe with a Hep2o coupling.

Next point of attack would be 15mm pipework to the cold rads. If you can get at the ends of the runs then you could replace the pipework, which I assume is copper, with Hep2o, even with 22mm if there's room, reducing to 15mm just before the rads.

That's all I can think of. Although I'm confused as to why the pump and MZV were replaced, and curious to know the colour of water than came out when you replaced them...

 

[notaplumber1967]

Marvellously clear images and description!

Very kind of you.

what's all the white stuff lying on the pump?

I'ts just dust from some recent decorating.

I replaced the pump a few months back because, A; it was getting a bit noisy and B; I thought it would cure this problem. The plumber that looked at the system last said he would need to replace the valve before he could test the system

Thanks for all that info, it will be very helpful. I am starting to build up a clear picture now of what will be involved in sorting this out. I can let you know what happens if you like. Thanks again.

 

[MANDATE]

Please do!

 

[notaplumber1967]

YEASSSS!! WHOOO!!!
I've done it! All my rads are working and there is no pump over, even with the pump on no.3.
Well done Softus and thankyou, it was a blockage, it was a piece of wood. It was stuck in the flow pipe at a T joint near the two rads that wouldn't work. I cut the pipes and a load of sludge came out along with the bit of wood. It must have been stuck in there for 10 years (thats when the system was installed). I would guess that the plumber pushed the pipe under the floor and the bit of wood went in the end.
The first thing I did was cut the short horizontal section of 22mm pipework just above the pump to see if that was blocked. It was a bit sludged up but not blocked. Next thing was to cut the pipes where they were cold. I cut the flow pipe first and after finding the bit of wood I didn't bother with the return.

Thanks for your help guys. I'm off to have long cold beer, I've been at it since 8 this morning. Cheers.