New Combi - One Pipe System

[Johnny8718]

Hi All.

Apologies, I replied to an old post earlier but decided that it may be better to add a new thread. I had a firm give me a quote, stating that I could have a new combi without having to change the pipework, saving me about £500 on the bill. They have come on recommendation and I dont think for one minute that they arent up to the job or would start a job without being prepared to make sure that it is right.

The problem is this. They have fitted a Potterton Apollo 30KW. When it pumps the water around the system, the radiators do not get fully hot. The plumber believes that the pump in the combi (much more powerful than the pump which was connected inline to the 22mm pipe from the Baxi back boiler) is firing the water around the circuit at such a speed that the radiators are only getting hot-ish. He explained that the water at speed will travel the path of least resistance and in effect the water is merely travelling around the circuit without really having the opportnity to enter the parallel branches at the rads.

The combi is showing that the water is getting up to 80ish degrees and the 22mm pipe is extremely hot to the touch.

The plumber will be coming back at the weekend to remove a section of the pipe at the bottom of each rad, blanking each end and therefore forcing the water through each rad in turn. The system will become serial which I understand is not the best. I'm not unduly concerned about this as I can have the room stats removed and have a system which more or less works?

Albeit this will not be ideal. To give me breathing space prior to re-piping the house, does all of this seem plausible? As a DIY'er I feel satisfied that this is the issue. Your expert views would be very much appreciated.

Thanks, John.

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[Nige F]

The plumber will be coming back at the weekend to remove a section of the pipe at the bottom of each rad, blanking each end and therefore forcing the water through each rad in turn. The system will become serial which I understand is not the best. I'm not unduly concerned about this as I can have the room stats removed and have a system which more or less works?

If you`re happy with something that more or les works then I`m happy for you , more or less . Wouldn`t be how I done it tho`

 

[Johnny8718]

[/quote] If you`re happy with something that more or les works then I`m happy for you , more or less . Wouldn`t be how I done it tho` [/quote]

I'll have that - and I fully appreciate that it wont work like a two pipe. But I am where I am. I cant afford to re-pipe the house just yet and tend to believe the plumber and his explanantion of what is going on. I just wondered if anyone had any other view, other than a few lines of sarcasm.

Thanks, John.

 

[plumbarius]

Hello Johnny, In the late 50s early 60s most systems where done like yours and a lot where done in one end of rad then out the other end, so if you turned one rad off they all went cold,I would not go down that route?
We often used swept tees or in my view the best way is to put an elbow
on the 22 pipe pointing up to the rad then a 22 by15 tee and run the 22 bypass under rad, do the same at the other end of rad and go round each rad in turn, You can then use your TRVs to control each room.
If the rads are sized right it will work fine make sure the system is clean
and fit a filter on the return to boiler and remember in my experience a large number of two pipe systems are not balanced right and defeat the object of effiecency.
Your Plumber should know what I mean.
Thanks Alex.

 

[ianmcd]

You should have spent the £500 that you so called saved and had a two pipe system installed it would pay for itself in a year what you have is very old design technology powered by an up to date boiler, the two dont mix Im afraid

 

[Johnny8718]

Hello Johnny, In the late 50s early 60s most systems where done like yours and a lot where done in one end of rad then out the other end, so if you turned one rad off they all went cold,I would not go down that route?
We often used swept tees or in my view the best way is to put an elbow
on the 22 pipe pointing up to the rad then a 22 by15 tee and run the 22 bypass under rad, do the same at the other end of rad and go round each rad in turn, You can then use your TRVs to control each room.
If the rads are sized right it will work fine make sure the system is clean
and fit a filter on the return to boiler and remember in my experience a large number of two pipe systems are not balanced right and defeat the object of effiecency.
Your Plumber should know what I mean.
Thanks Alex.

Alex.

Thanks very much for the reply. The heating system was fitted in 1967 and has been changed, updated and messed with ever since. Apart from the backboiler being very inefficient, the system worked perfectly well.

The piping as you explain it is as it is now. A 22mm pipe running around the house, with 15mm tails coming off upwards at each rad. I have stats on all but the bathroom.

My plumber tells me that the reason that the water isn't syphoning into the rads is because its travelling around the 22mm loop too quickly (he didn't anticipate this by the way). Do you think this is plausible?

His plan is to cut the 22mm pipe under each rad and cap the ends, therefore turning the system into series. Therefore the 22mm pipe will in effect elbow upwards to 15mm, enter the rad and will leave at 15mm before elbowing back into the loop again at 22mm. We have tried balancing it but it just isn't working.

Thanks, John.

 

[algas]

Rather than cap both ends get him to fit a gate valve so that the water can be made to go through the rads but still make the circuit if you understand me.

 

[Johnny8718]

Rather than cap both ends get him to fit a gate valve so that the water can be made to go through the rads but still make the circuit if you understand me.

...........such as a Ballofix valve??

 

[Agile]

I would use an iso valve.

They have a restriction which will creeate a pressure differential which will encourage flow through the rads.

In spite of what Ian, says many single pipe systems can work very well.


The usualy problem is that the rads are unbdersized. I combat that problem by fitting a large central rad connected as a parallel. Typically in the dowstairs hall.

Tony

 

[plumbarius]

Johnny It is plausable what is the pump head in feet what pump was fitted before, I have never fitted a Combi I presume it pumps round the hot water heat exchanger as well so it might be quite a big head, I would not put any restrction on the 22mm pipe at all you are defeating the object
ask your Plumber to try 1 rad like i said and try it, The pipe you cut out should fit between the tees, are you sure it is 22mm and not 3/4 "
Agile idea of a big rad in hall is a good idea.
Let us know how you get on, We are still learning all our lives.
Thanks Alex.

 

[Johnny8718]

Will do! I know the obvious is to repipe, but money and mess is the problem.

I will let my plumber work his magic, mention your comments and let you know how we get on.

Thank you very much for your help so far!

John.

 

[mogget]

If a two pipe system would just be too expensive, I would second the idea of a gate valve fitted in the 22mm under each rad. You would have the flexibility to turn radiators off as well as getting the system into some kind of balance. Not ideal but it would work.

 

[plumbarius]

Johnny, Was the pump on the return on the old system we always fitted them on return in 60s they would sieze up if fitted on the flow, Ask your Plumber to check it is not flowing the other way round to what it was, if it is it could be closing the TVR`s. another possibility is the rads are full of sludge the system should have been cleaned before he fitted the Combi,
the first job for the Plumber is to take a rad off and wash it out with a hose pipe, I am still of the opinion if it worked before it should work now
even with a bigger pump head, It will be interesting to see what the time served Plumbers think on this forum.
Thanks Alex.

 

[doitall]

I got as far as removing the link pipe and stopped.

Throw them off the job now before they make it worse.

I see you have stats on the rads, are they new, if so, a pound to a penny they are the wrong type. more information about them please

Do NOT let them remove the link pipe between each rad.

 

[Johnny8718]

Hi All.

In answer to your questions, the plumber did consider that the pump may be closing the valves, as obviously the combi is not in the chimney breast and as a result the pump is situated in a different part of the house now. He ran the heating once, realised that this may be an issue and reversed/swapped the flow and return in the loft. It did not seem to make much difference. However, the valves are bi-directional.

The system is clean and was flushed.

I take your points. I am well and truly miffed. The only saving grace is that he comes on recommendation from a number of sources and believe it or not is reputable. I am now considering asking him to convert to two pipe ASAP as although it will cost more, it seems the only solution.

He did offer to fit the boiler to my perfectly working one pipe system out of good faith to ease the job for him and make life easier for me. I think its a judgement call gone wrong.

Your views are very much appreciated.

John.