Central Heating - Blocked 22mm return pipe?

[VinMK73]

Hello all. I've just joined, was going to post in the new members forum, but the first site generated email sent me here...

I am here, as have a challenging and interesting problem, which I'll try as best to describe below keeping to the point and as short as possible, to avoid boring any of you.

So...

Ideal FF250 Classic, old but been working fine. Changed the fan that failed and PRV valve last winter as was leaking.
Heating performance last winter (2021/22) degraded, lost heat to downstairs rads. Old rads were original and a couple showing some rust.
New rads all round Sept 2021.
Sealed / pressured system FYI.

Had an expensive powerflush in Jan 2022 which I know was done incorrectly, as they just plugged it in and left it running 3.5 hours, occasionally switching direction. No agitation or isolation of any rads.

Bolier comes on for approx 1min 30 seconds, kettles, switches off.

Slowly heats the water but was getting no heat to rads at all.

Replaced 3 way valve and pump.

Microbore to rads, 22mm main pipes

Flow pipe looked gungy, sludge in there. Return pipes to boiler I think are my problem. Return pipe into boiler only gets luke warm to mildly hot to touch. Flow pipe piping hot. So Im guessing the return is gunged up and partially or fully blocked.

So, I spent all of yesterday, having fully drained the system, and shutting off the valves on each rad, for all rads, one by one flushing each rad from the refill loop on/off.

I used a rad valve, attached to hose, and blasted water through each rad, with just one valve open at a time, switching until water ran clear. Got quite a lot of very dark nasty looking water out of each and every rad in the house. The water flows clear from all rads now.
Water pressure through each rad was also good, didnt look to be any issue. So I dont think the microbore is blocked or restrictive.

Once all the rads were fully flushed, and after doing each rad, I shut them off, so just the rad I was flushing had flow, once done I pressurised the system and filled the rads. Added 1ltr of cleaner too.

Fired up the boiler, let it run, got 3 minutes out of the first burn then back to 1min 30 secs. Slowly it heated the hot water, and upstairs rads got quite warm. Flow pipe to rads which runs through airing cupboard, too hot to touch. Return pipe in airing cupboard and top of boiler, luke warm.


I think it is the 22mm return pipe, from the airing cupboard and hot water tanks, that I think the rads also tee into, is blocked or heavily restricted.

The company that did the powerflush also felt that was likely to be the cause as the powerflush didnt work.

The distance between the boiler and the airing cupboard is about 7m-8m and of course under the fairly newly carpeted floor.

The only thing I can think left to try, is to cut the return pipe at both ends and try somehow to blast it through.

The alternative is to forget gas heating and replace with elec rads, but elec is getting a bit pricey!

Would any of you have any ideas of what options I may have left? Tried to get a couple of local plumbers to take a look and quote to fix, only one came out in the end and he never got back to me
The company who did the powerflush, i wont use again as I just dont feel they did it properly on the day, and certainly didnt follow anything like the process many YouTube videos of other companies show.

Any response and feedback would be appreciated.

Cheers
Vin

 

[SimonG]

I wont do a power flush on microbe, cant gaurantee good results.

Are you sure it's not trapped air?

Take all rads out into the garden and stick a hose in them.

Worth a try before you have to start cutting sections of pipe out.

 

[Ric2013]

So you're flushing through the pipework with a hose. Not a bad idea. Bear in mind this tests the flow through the pipe and the radiator at the same time, so you won't know which is blocked.

Where is your flushing water going, though? Can you prove or disprove that there is an uninterrupted path for the water to flow all the way back to the boiler along both flow and return sides?

When you say the return gets lukewarm, that will be probably because the water is running around the circuit slowly and having time to get quite cool before it gets back to the boiler. It could do this even if the blockage were in the pump on the flow or because the thermostatic radiator valves have jammed almost shut.

Keep using logic (which I see you have been doing) before you jump to conclusions that a pipe is completely blocked and test all theories you develop (even if means temporarily cutting the boiler out of the system entirely, sticking a hose on one end of the primaries and seeing how far the flow can get around the system).

Not sure what cleaner you've added to the system, but bear in mind that if it successfully frees off some gunk, that gunk will then be circulating in the water and will need flushing out.

 

[VinMK73]

I wont do a power flush on microbe, cant gaurantee good results.

Are you sure it's not trapped air?

Take all rads out into the garden and stick a hose in them.

Worth a try before you have to start cutting sections of pipe out.

Hi Simon
Thanks for the response.
Pretty sure its not trapped air, I've fully drained down and refilled many times now, ensuring that fully bleed at all points until water gushes through.
Rads were brand new in Oct 2021.
I have cut a section of flow pipe out already, to discover it was pretty gunky. Somehow, there seems to be a lot of crud in my system.

 

[VinMK73]

So you're flushing through the pipework with a hose. Not a bad idea. Bear in mind this tests the flow through the pipe and the radiator at the same time, so you won't know which is blocked.

Where is your flushing water going, though? Can you prove or disprove that there is an uninterrupted path for the water to flow all the way back to the boiler along both flow and return sides?

When you say the return gets lukewarm, that will be probably because the water is running around the circuit slowly and having time to get quite cool before it gets back to the boiler. It could do this even if the blockage were in the pump on the flow or because the thermostatic radiator valves have jammed almost shut.

Keep using logic (which I see you have been doing) before you jump to conclusions that a pipe is completely blocked and test all theories you develop (even if means temporarily cutting the boiler out of the system entirely, sticking a hose on one end of the primaries and seeing how far the flow can get around the system).

Not sure what cleaner you've added to the system, but bear in mind that if it successfully frees off some gunk, that gunk will then be circulating in the water and will need flushing out.

Thanks for the response Ric.

So the hose is the exit. I moved that hose to the same position on each rad, one by one, and forced the water through by using the refill / pressure loop, leaving it open until the water ran clear.
I did this with only one valve open on the rad, close that once clear, then open the other valve on the rad, and repeat for about 10-15 mins total per rad.

I do not have TRVs, just basic open/close lockshield types.

To take the boiler out the loop, which I've considered, I have to cut the return pipe above the boiler. No problem with the cut, but space is limited as the boiler is mounted close to the ceiling. It will be a tight job and definitely will involve cutting a section of ceiling out, to get a proper good connection once putting back together.

But, the theory there would be to then cut the return pipe in the airing cupboard to and with a hose each end, see if I can get good flow and clear that pipe.

The oddity is, for my understanding of how this all works, is that from the hot water return pipe, that comes back out the bottom of the immersion tank, there are 2 tee'd off sections that drop through the floor, which I've no idea where they would go, if it's a direct return to the boiler.

Regarding the cleaner, as Im just going to drain down and flush again, I used the Corgi cleaner, as £9 a litre. I'd had MCP in the system before, after the powerflush. Not sure how much actually got in as that was the powerflush company and most of it ended up on the floor, they didnt seem to know how to get it into the system!

Once I've drained down in the next couple of days, I was going to add 2 litres of CalMag that I have, as can leave that in longer to work. But it wont clear an actual blocked pipe, it might eat away at it over time if the water is coming back at all on the return. But winter is here and I dont have too much time to try fix this...

 

[king of pipes]

Is this open vented ? a small tank in your loft space to fill your system ? I'm guessing it is does the system fill ok ? Post a couple of pictures of your system please . Kop

 

[Ric2013]

Well, if you're getting flow through to both the valves on each radiator from the boiler, it would appear that there is an uninterrupted path all the way from the boiler along the flow and along the return. But it's possible that there is a blockage on the primary flow or return and the water is flowing through other radiators (or a bypass) to get back to the fill loop. Shutting other radiator control valves would be one way to find out if this is the case.

Tees off the cylinder return sound interesting. Could be fed to a towel rail(s) (clutching at straws here) or close coupled tees feeding... what? Could simply be redundant pipework from an earlier incarnation of the system.

 

[VinMK73]

Is this open vented ? a small tank in your loft space to fill your system ? I'm guessing it is does the system fill ok ? Post a couple of pictures of your system please . Kop

Thanks for the response.

There is a F&E tank in the loft that is for the immersion tank and hot water. There is no other tanks and it's not a vented system so much as my knowledge goes, the CH is sealed.

Few pics of the airing cupboard attached.

You can see behind the red lever from the return from the tank, there is a tee as there is another about 12 inches down the pipe.

Ignore the poor bit of pipe work off the air bleed valve, plumber who replaced the tank, left it like that.
The vertical pipe with the end cap, closest / towards the front, I put that in temporarily to more easily be able to get cleaner into the system.

Mains water fill loop at the back, which is what I was turning on to flush the rads and system through.

 

[VinMK73]

Well, if you're getting flow through to both the valves on each radiator from the boiler, it would appear that there is an uninterrupted path all the way from the boiler along the flow and along the return. But it's possible that there is a blockage on the primary flow or return and the water is flowing through other radiators (or a bypass) to get back to the fill loop. Shutting other radiator control valves would be one way to find out if this is the case.

Tees off the cylinder return sound interesting. Could be fed to a towel rail(s) (clutching at straws here) or close coupled tees feeding... what? Could simply be redundant pipework from an earlier incarnation of the system.

I think I am getting flow through both, flow is hot on some, hot/warm on others. Return not so hot. Assuming I am getting them the right way around, given the flow would be the hottest. valves are wide open both sides presently on all upstairs rads, just to figure it out. Its not balanced, but zero heat to downstairs rads still.
I have tried them all closed, isolated and brining them on one by one, starting downstairs, but no heat to the downstairs at all.

See the pics above of the tees off main return. Im stumped by that.

 

[ShaunCorbs]

So if you turn all upstairs off no flow to downstairs?