How to identify a one pipe system

[Scott_D]

Anyone got any tips on identifying a one pipe system?
While quoting you cant start lifting floorboards for obvious reasons.
I went to do a quote last night, they want an open vent/heat only boiler and cylinder changed for a combi and TRVs added, 3 bed 10 radiator house.
First thing I noticed was a 28mm flow and return for heating and the first radiator from the boiler had 15mm tails coming up through the floorboards but the tails were joined together with 15mm under the radiator creating a bypass.
Everything else on show looked like a standard setup.

 

[SafeGasInstall]

Single Pipe Central Heating Systems

 

[Scott_D]

Thanks for the link.
I understand how it works etc, just wanted to know if there were any clues to it being a one pipe system when there isnt much on show.

 

[Killy Bing]

if your not sure of course you can lift the floor boards.
point out that if its a one pipe system it may not be suitible.

if they wont allow you then think of the problems once you start. its a perfectly reasonable request.

 

[SafeGasInstall]

have a look in the airing cupboard , usually in London they have been plumbed on a c plan with the old thermostatic valve going to cylinder , also common is to have the primatic cylinder and there will be a one tank in the loft , and when you drain ch , system will drain the cwst too

 

[happyflyer]

Thanks for the link.
I understand how it works etc, just wanted to know if there were any clues to it being a one pipe system when there isnt much on show.

Scott,

It's easy to spot the difference, when you turn on the heating from cold on a single pipe (PUMPED) system the return will get warm quickly, this is because the water gets back to the boiler sharpish, and is not being pumped in and out the radiator, the cold water in the rads take's a long to rise and if you grab a flow and return one in each hand you will notice the very slow rise in temperature in the return compared to the flow. On a two pipe system you will notice the flow and return on heating up very close to each other. Make sure you have both hands on, one on the flow and one on the return, don't keep feeling one and then the other with the same hand, if you use both hands you brain is between the two and it will work out the difference in temps, have have seen so many engineer using the same hand and you cannot detect small temperatures that way, if you have a twin channel temp sensor even better still, the 28 mm tube might also give it away,its single pipe, hope this helps

Tony

 

[Scott_D]

Thanks for the info. I will have to go and investigate.
Get them to clear out the airing cupboard and take my Kane FGA and temperature clamps.

 

[Derek Hardman]

For visual clues there is always the high level valve at one end of the radiator (flow), in bedrooms where there is little rise and fall in the pipework, the radiators would be hung tilted (higher at one end) to aid heat rising, same in solid floors, not enough depth to rise and fall the pipes, so the rads were hung on a kilter.

 

[plumber0808]

I personally just get the feeling and can tell.

There are some weird and wonderful heating systems out there, i was working on one before Christmas I had a few rads to add on a very large system. I spotted one on a 1 pipe straight away so thought they were all like it but that was the only one out of about 20 odd rads.
The pipework was partly buried in concrete so when the system was partially updated they left it on a 1 pipe

I changed it and fitted a towel rail in its place

 

[Scott_D]

All the radiators were bottom entry, opposite ends.
Everything looked normal except for the bypass under one rad and the 28mm pipe.
Always a pain to spend hours on a quote you may never win.

 

[leethegasman]

The best thing to cover yourself if you think it may be one pipe system is to put a note on your quote if at time of installation it is found to be a one pipe system this will be quoted for.but if a working boiler test temps like said in previous post.
I have had jobs where they have been all one pipe,one pipe upstairs only,one pipe downstairs only,and a mixture of both.

 

[SafeGasInstall]

All the radiators were bottom entry, opposite ends.
Everything looked normal except for the bypass under one rad and the 28mm pipe.
Always a pain to spend hours on a quote you may never win.

i worked on a HA and there was many two pipe system with bypass fitted under bathroom rad which was piped on the hot water on the old y plan



by pas had a 15mm service valve

 

[plumber0808]

It's not ideal but lift a floor board in front of one and you will know straight away.

you can fit a combi onto a one pipe if done correctly, also manufacturer permitting.

 

[Scott_D]

The best thing to cover yourself if you think it may be one pipe system is to put a note on your quote if at time of installation it is found to be a one pipe system this will be quoted for.but if a working boiler test temps like said in previous post.
I have had jobs where they have been all one pipe,one pipe upstairs only,one pipe downstairs only,and a mixture of both.

Any issues when converting to a sealed system with a condensing boiler? Or did you change to two pipe

 

[leethegasman]

Any issues when converting to a sealed system with a condensing boiler? Or did you change to two pipe

Changed to two pipe when installing new boiler ,except for one advised customer but they did not wont it changing.

 

[happyflyer]

Fitting a low water content boiler onto a 28 mm single pipe system is like having one big bypass loop, if you where to fit electronic thermostatic radiators valves you would not need any zone valve, the only problem you have you still have water flow in the 28 mm system during the summer whilst you have the hot water on, nice to re pipe the system if you can all the same, but don't take out a copper system and replace it with plastic LOL :2guns:some also said lift a FB straight in front of a radiator, most good plumbers would smell a one pipe system stood at the front door :waving:

 

[leethegasman]

I am sure we have all founded the unexpected when carrying out are work.some times like you say you can spot it at the front door,but in some cases you can not tell where the two pipes going in to a floor from radiators go with no visible drops.(and if crystal ball has been left at home it make the job even harder)