Cold radiators in loft

[Stigster]

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.

 

[ShaunCorbs]

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

 

[Stigster]

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.

 

[milleniumaire]

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.

 

[ShaunCorbs]

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

 

[milleniumaire]

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.

 

[ShaunCorbs]

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

 

[milleniumaire]

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.

 

[milleniumaire]

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:

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!

 

[centralheatking]

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