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Hi, I've have a problem with my CH system for around 18 months now and it's time to get it sorted. Here's a diagram showing our current heating system:

Current Central and Underfloor Heating Layout.jpg


The house is 21 years old and the loft extension was performed around 15 years ago. As you can see they simply extended the existing 15mm pipes up into the loft and then split them. The Vaillant equipment is 8 years old and still going well. We had the UFH installed 5 years ago as part of a kitchen extension.

Only one of the radiators in the loft gets a little warm, never hot and the other radiator and towel rail are always cold, so there's clearly a blockage or two. I have accessed the 15mm flow and return pipes to the loft at the point they are connected under the bathroom floor and the flow pipe gets very hot, the return pipe is barely warm. I have tried closing all valves to force the water into the loft pipes but it makes no difference.

I have been considering replacing the existing 15mm pipes into the loft with 22m pipes and connect them up earlier as is shown in the following diagram:

Fix Loft Issue Revised Layout.jpg


Obviously I'll have to resolve the existing blockages in the loft pipework.

My diagram may not be accurate for the Ground floor radiators. It currently shows the flow going into the final toilet radiator and then back out into the return. Is this how you would expect the pipes to be connected at the end of a run or would the flow become the return? The 1st Floor to loft connections shown in the first diagram are exactly as they are plumbed. So, if all the loft radiators were turned off, there's no way for the flow to return to the boiler (I think!). In fact, in my diagram the only way for the flow to become the return is through a radiator. Not sure how accurate this is.

A couple of concerns:
1. Will the boiler pump be able to handle the additional 22mm pipes running into the loft?
2. Should I consider re-routing (new) pipes around the loft as the "star" connection currently used looks to be a limitation to my untrained eye.

Thanks in advance for your thoughts.
 
Great diagrams well done. 15mm pipe is as you suspect the limitation. Putting in 22mm
will put less strain on the pump. Yes pipe up the loft with conventional flow and return.
centralheatking
 
No matter what you shut off, every rad has a flow and return path to boiler.

Undersized pipework is an issue but you'd still expect them to all heat up fairly evenly if not as hot as they should. It does sound like a possible airlock as Gasmk1 says.
[automerge]1571572782[/automerge]
Another thought, I know you have tried closing all the other rads down to force out any airlocks. However when that fails to work I would temporarily increase the system pressure to 2 or 2.5 bar which will compress down any slugs of air in the system and give the pump a better chance at moving air to a radiator where it can be bled off.

Return to normal operating pressure after trying that of course.
 
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Have you actually bled the rads could be as simple as air or an air lock
No matter what you shut off, every rad has a flow and return path to boiler.

Undersized pipework is an issue but you'd still expect them to all heat up fairly evenly if not as hot as they should. It does sound like a possible airlock as Gasmk1 says.

Hi guys, thanks for responding.

When I first encountered the issue I assumed it was the TRV's that were sticking on the two radiators and so replaced them. While doing this I removed both radiators and gave them a good flush through outside. There was a fair amount of black gunge in them, despite having a magnacelan on the system (oops, forgot to include that in my diagrams :) ).

Unfortunately, this didn't make any difference. My suspicion is the water flow in these radiators is so poor due to the 15mm pipes connected to the very end of the pipe run and the "star" method of connecting them up, that gunge has collected in the pipes feeding the radiators.

If it was simply air, couldn't that be flushed through by closing off every other radiator to increase the flow/pressure? I have tried this a couple of times.

Great diagrams well done. 15mm pipe is as you suspect the limitation. Putting in 22mm
will put less strain on the pump. Yes pipe up the loft with conventional flow and return.
centralheatking

Thanks for posting. It's strange as I imagined a larger 22mm pipe would put more strain on the pump as it has a larger volume of water to move through the pipe, especially as this new run of 22mm has to go from one end of the house to the other, then up a floor.
 
If it was simply air, couldn't that be flushed through by closing off every other radiator to increase the flow/pressure? I have tried this a couple of times.

Sometimes the slug of air is too long and compressible to be moved by the pump even under ideal circumstances with the other rads closed. That's why I suggested trying with the pressure increased. It compresses the trapped bubble giving the pump a better chance to move it to a rad.

I only suggest it because it sometimes works and is easy enough to do. Always try the simpler things first, which I appreciate you have been doing but that's one more to try.
 
Another thought, I know you have tried closing all the other rads down to force out any airlocks. However when that fails to work I would temporarily increase the system pressure to 2 or 2.5 bar which will compress down any slugs of air in the system and give the pump a better chance at moving air to a radiator where it can be bled off.

Return to normal operating pressure after trying that of course.

Sorry Stigster I didn't see this original post. I will definitely try this. I assume to increase the system pressure it's simply a case of letting more water into the system and monitoring the pressure gauge. While the boiler is running hot, the pressure is at 1.8 bar, so I guess I could increase this to 2.5 bar and then afterwards let water out through the magnaclean connections.
 
Sometimes the slug of air is too long and compressible to be moved by the pump even under ideal circumstances with the other rads closed. That's why I suggested trying with the pressure increased. It compresses the trapped bubble giving the pump a better chance to move it to a rad.

I only suggest it because it sometimes works and is easy enough to do. Always try the simpler things first, which I appreciate you have been doing but that's one more to try.
You could shoot the system up with mains pressure ...find a rad with a good type mt cock
connect hose with a jubilee clip and put the other end on to outside tap. close off boiler
flow and return then shoot it up with mains pressure water, start at the bottom and bleed every rad going upwards and along so the last rad is highest and furtherest away.
In case anybody wants to do this with open vented it works but be carefull not to overfill
the F & E tank. blip the pump on and off ...its a bit like heart surgery for heating systems.
then undo the lot and maybe dump all the water and do again..its not rocket science
centralheatking
 
You could shoot the system up with mains pressure ...find a rad with a good type mt cock
connect hose with a jubilee clip and put the other end on to outside tap. close off boiler
flow and return then shoot it up with mains pressure water, start at the bottom and bleed every rad going upwards and along so the last rad is highest and furtherest away.
In case anybody wants to do this with open vented it works but be carefull not to overfill
the F & E tank. blip the pump on and off ...its a bit like heart surgery for heating systems.
then undo the lot and maybe dump all the water and do again..its not rocket science
centralheatking
It's interesting you have mentioned using mains pressure as I've read about someone doing this to remove a blockage caused by sludge.

In my attempt to remove the blockage I was going to do the following:
1. Empty some water from the CH system, enough to empty the loft radiators and loft pipe work, but ideally still keep the bedroom radiators full. This will be a guessing game!
2. Disconnect the loft radiator piping from the two 15mm pipes currently feeding the loft from the bathroom and then connect these two pipes together. At this point I have isolated the loft radiators from the rest of the system.
3. Re-pressurise the system so that it can continue to be used in the rest of the house.

I then have 2 pipes going to each radiator in the loft and I can connect, in turn, each radiator circuit to a hose pipe as you have suggested. As it is the loft, I would need a long piece of hose (just bought a 30m hose) connected to the outside tap, so I'm a little unsure what pressure I could achieve given it is going up to the 2nd floor. The other side of the circuit I would connect to a hose that terminated in the loft toilet. I can then turn on the outside tap and see if any water flows into a toilet. For the cold towel rail and cold radiator I suspect nothing will flow through. For the warm radiator I may get a trickle.

I'm not sure what the mains water pressures involved would be in doing this but suspect it will still be higher than that produced by the CH system.

If this fails I was planning to access the piping under each radiator. I haven't mentioned before, but the 15mm feed and return pipes to the loft are copper (as is the rest of the house), however, the 15mm pipes to the loft radiators are all plastic (and yes I've checked they are the correct CH pipes given this was installed 15 years ago). My understanding of plastic piping is that the joints, especially elbows, can reduce the diameter of the pipe, so I suspect if there is a blockage it is likely to be on the elbows underneath each radiator, where the plastic pipe is connected to the copper tails going to the radiator valves. Of course this is all guesswork :)
 
..... I did get a company round to quote for power flushing the system as I thought this might clear the loft radiators. However, they told me it wouldn't and therefore not to waste my money, which was very honest of them!
[automerge]1571586047[/automerge]
...... Yes pipe up the loft with conventional flow and return.
centralheatking

So, the loft pipes would be run as follows?

Fix Loft Issue Revised Layout 2.jpg


Or, should the flow be connected to the return to ensure even when all loft radiator valves were closed, the flow would cycle back round to the boiler:

Loft Flow connected to Return.JPG


I confess, I haven't been able to find any CH diagrams that show this and maybe the "hot" water in the flow shouldn't be allowed to simply return to the boiler.
 
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Yes of course set up a shoot up...in down below and find another outlet to make a curcuit
I usually put the output hose onto a hard surface ..road whatever ..so you can see what
ferric sludge comes out and when it goes clear. I have being doing this method for 20 + years
it cheap and works. basically the pump boys dont want you to know about this method
because of ££££££ it works . centralheatking
 
... I did get a company round to quote for power flushing the system as I thought this might clear the loft radiators. However, they told me it wouldn't and therefore not to waste my money, which was very honest of them!
[automerge]1571586047[/automerge]


So, the loft pipes would be run as follows?

View attachment 40985

Or, should the flow be connected to the return to ensure even when all loft radiator valves were closed, the flow would cycle back round to the boiler:

View attachment 40986

I confess, I haven't been able to find any CH diagrams that show this and maybe the "hot" water in the flow shouldn't be allowed to simply return to the boiler.
Maybe too many rads on the middle floor set up if its on 15mm flow and rtn but in principle
its all dandy ...carry on ...chking
 
Having done some Googling, I think my second diagram, showing the flow connected to the return, is essentially a bypass at the furthest end of the CH loft piping. From what I can gather this isn't required, or particularly good practice. Also, my ecoTEC 637 system boiler has a built in bypass valve.

So, assuming I connect up the loft radiators as shown in the first diagram, if ALL the loft radiators and towel rail are closed, the flow of hot water will simply "stop" in the loft, but will continue on the first and ground floor.
 
I'd take the rads off first, put pieces of pipe between the valves. Turn all other radiators off, make sure the water and UFH is turned off, ensure all bypass valves are closed off and run it. If the pipework gets hot then you either need to repipe in 22mm or just get a bigger pump (Grunfos do a light commerical one which is brilliant) - the latter would be your easier option.

You have to remember the pump in the boiler is only designed to give 6 meter head too so might not be big enough for your system. You will also benefit putting the pump in 100% output mode on the computer on the Vaillant boiler. The internal bypass on the Vaillant might also not be set correctly (Read the MI) however you will have to get a GSR engineer in to alter that as it requires removing the front cover of the boiler.

If it doesn't get hot at all then you've got an issue with the pipes going to the loft. If they're done in plastic they could be kinked over somewhere under a floor etc...
 
Also, with a cold system, the expansion vessel pressure should be > 0.8/1 bar to overcome the static head of ~ 0.7 bar due to the loft location, also making sure that the pressure is changing with hot and cold conditions in case the gauge is blocked/faulty.
 
I would try bleeding the rads at the top of the system first, air is less dense that water so all the would collect up there.
 
Having done some Googling, I think my second diagram, showing the flow connected to the return, is essentially a bypass at the furthest end of the CH loft piping. From what I can gather this isn't required, or particularly good practice. Also, my ecoTEC 637 system boiler has a built in bypass valve.

So, assuming I connect up the loft radiators as shown in the first diagram, if ALL the loft radiators and towel rail are closed, the flow of hot water will simply "stop" in the loft, but will continue on the first and ground floor.

That is correct. As you have worked out, if you close all the rads on the loft part of the system, the water will stop flowing through the main flow and return but only in that section. The rest flows perfectly fine and normal. Linking the flow and return will introduce a bypass, again as you have realised and this may stop the rads in the loft from working at all as the flow will take the path of least resistance and probably fail to flow through the rad at all or at least very poorly.
 
have you tried turning all the other rads off via there trvs do the loft rads get warm / start to?
 
have you tried turning all the other rads off via there trvs do the loft rads get warm / start to?

He mentioned that in his first post. Don't worry though, I asked the same question having missed where he said that too and had to edit my post.
 
You have to remember the pump in the boiler is only designed to give 6 meter head too so might not be big enough for your system. You will also benefit putting the pump in 100% output mode on the computer on the Vaillant boiler. The internal bypass on the Vaillant might also not be set correctly (Read the MI) however you will have to get a 'Registered Professional Gas Engineer' engineer in to alter that as it requires removing the front cover of the boiler.
Thanks for the info. This is a little beyond my knowledge level, but I will consider it after I have tried everything else, if the issue persists.

In my case, it is actually easier for me to lay some new 22mm pipe as I'm currently renovating my bathroom, which involves lifting a lot of floor boards. This is the reason why I've decided to attempt to resolve the loft issue now, while I've got access to the bathroom CH pipes that feed the loft.

Our boiler is due a service next month, so I will discuss it with the heating engineer and see what he says, however, I hope to have the loft radiators working before then.

have you tried turning all the other rads off via there trvs do the loft rads get warm / start to?

Yes, I have tried this a couple of times and when the "power flushing guy" came round, he also tried it. I think he assumed he would easily be able to clear the blockage, but it made no difference.

I will try this again however but with the pressure raised to 2.5 bar as suggested by Stigster.
 
Thanks for the info. This is a little beyond my knowledge level, but I will consider it after I have tried everything else, if the issue persists.

In my case, it is actually easier for me to lay some new 22mm pipe as I'm currently renovating my bathroom, which involves lifting a lot of floor boards. This is the reason why I've decided to attempt to resolve the loft issue now, while I've got access to the bathroom CH pipes that feed the loft.

Our boiler is due a service next month, so I will discuss it with the heating engineer and see what he says, however, I hope to have the loft radiators working before then.



Yes, I have tried this a couple of times and when the "power flushing guy" came round, he also tried it. I think he assumed he would easily be able to clear the blockage, but it made no difference.

I will try this again however but with the pressure raised to 2.5 bar as suggested by Stigster.

Pull one of the rads off

Open the flow into a bucket does much water come out and the pressure drop in the system

Do the same test on the return will tell you which one could be blocked
 
Pull one of the rads off

Open the flow into a bucket does much water come out and the pressure drop in the system

Do the same test on the return will tell you which one could be blocked

Thanks Shaun. You have just reminded me that last year after I had replaced the TRV's on both radiators, I tried this. The water from the piping connected to the lockshield side of the radiator (I would assume the return pipe) was much slower, however, there was water coming out, which did confuse me as this suggested it wasn't blocked.
 
Thanks Shaun. You have just reminded me that last year after I had replaced the TRV's on both radiators, I tried this. The water from the piping connected to the lockshield side of the radiator (I would assume the return pipe) was much slower, however, there was water coming out, which did confuse me as this suggested it wasn't blocked.

Might be draining from the other rads etc close them off then test
 
Sorry Stigster I didn't see this original post. I will definitely try this. I assume to increase the system pressure it's simply a case of letting more water into the system and monitoring the pressure gauge. While the boiler is running hot, the pressure is at 1.8 bar, so I guess I could increase this to 2.5 bar and then afterwards let water out through the magnaclean connections.
Tried this tonight but increasing pressure didn't make any difference.

At the weekend I will drain the loft down and disconnect it from the rest of the heating system, then after removing the radiators try forcing mains pressure water through some of the pipes.
 
I had another go at flushing through last night, but the water is still only trickling through, so the pipe run I'm currently working on is still obviously blocked. After I poured out the water from the bucket, I was surprised to see this:

20191028_210441.jpg


20191028_210451.jpg


This is from only one pipe run of the 6 I have to flush!

Although I've flushed through one of the radiators outside, I may replace them both as they are around 15 years old. Not sure what to do about the chrome towel rail. I assume these can also corrode on the inside?

Not sure if this sludge in the loft pipes is purely from the loft radiators or if it will be from the whole house, but will have settled in the loft pipes due to the poor flow.

This amount of sludge explains why the radiators in the loft aren't warming!
 
I had another go at flushing through last night, but the water is still only trickling through, so the pipe run I'm currently working on is still obviously blocked. After I poured out the water from the bucket, I was surprised to see this:

View attachment 41184

View attachment 41185

This is from only one pipe run of the 6 I have to flush!

Although I've flushed through one of the radiators outside, I may replace them both as they are around 15 years old. Not sure what to do about the chrome towel rail. I assume these can also corrode on the inside?

Not sure if this sludge in the loft pipes is purely from the loft radiators or if it will be from the whole house, but will have settled in the loft pipes due to the poor flow.

This amount of sludge explains why the radiators in the loft aren't warming!
Well done so far, it gets easier with practice, look on the bright side, at least the sludge is black...brown sludge is very naughty. Remember when you think its all done it is not
at least two more passes...but think how much money you are saving and you know its been done. award yourself 4 tins of whatever straight away and a similar portion at the end with a takeaway...centralheatking
 
One radiator and associated pipes have now been cleaned out and reconnected to the CH system and it is working perfectly.

Just the towel rail and another radiator to go.....
 
I'm intrigued. What is brown sludge?
Oh sorry I missed this, my understanding is thus
1. Black Ferric Sludge occurs with a sealed system inc. an open vented system and needs to be dealt with.
2. Brown Ferric Sludge indicates that the system is continually introducing fresh water with air dissolved into it, maybe eg an open vented system is pumping over.
I tested this towards the end of my last house which I sold for demolition...I had an Eclipse MicroMag industrial filter on it when we deliberately left an mt cock slightly open the ch water turned from black to brown when we took the micromag out of circuit.
To explain my main workshop in that house had the boiler located there so we used to use it as a test vehicle for all sorts of things.
centralheatking
57670BB8-F25E-415D-95CE-7A6B3D3F0FEB.png
 
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2. Brown Ferric Sludge indicates that the system is continually introducing fresh water with air dissolved into it, maybe eg an open vented system is pumping over.
I did Google Brown sludge but only found references to car radiators.

As my system is sealed hopefully brown sludge won't be a problem, but I am alarmed at the amount of black sludge I have come across in the loft pipes and radiators, which is strange as the magnaclean never seems to get very clogged up. I need to check it again now that I've re-introduced one of the loft radiators.
 
I did Google Brown sludge but only found references to car radiators.

As my system is sealed hopefully brown sludge won't be a problem, but I am alarmed at the amount of black sludge I have come across in the loft pipes and radiators, which is strange as the magnaclean never seems to get very clogged up. I need to check it again now that I've re-introduced one of the loft radiators.
You are quite correct water cooled motor vehicles do suffer badly, we did look at automotive with Honeywell but there was no commercial traction so we both walked away It is not for me to criticise
any domestic magnetic and strainer type ch filters. Its been at least a decade when I designed some..domestic mag filters .not Magnaclean. You might go along your naughty radiators and visible pipes with a magnet and a soft rubber mallet...thats quite good
there is an adgitator tool which you can put on a domestic electric drill that was origionally my idea I dont know what they call it ...But I got paid for it as usual...nice holiday.
Chemicals will only maintain the status quo not remove the stuff ...a really good reverse pump out first is good...this should take two men all one day.
centralheatking
 
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