Single pipe system new combi boiler

[Matti5041]

Hi everyone. I’m a homeowner, in essence when we moved in we weren’t aware that our house was a single pipe system we have now found out after the water cylinder has packed in and developed a leak.
We have had a Heating engineer round who has advised us to fit a combi boiler doing away with the water tank and cylinder. He said there is a risk that it can cause leaks however said the risk was small.
Some of the pipe work in the house is new as there was an extention built but some is old.

How often in everyone’s experience does a new combi cause leaks and major problems in an old system.

Unfortunately taking up floors isn’t really an option as we have more or less renovated the house now all laminate and wood floors down etc.

If I had known at the start I would have replaced the heating as one of first jobs but we are were we are. Appreciate any advice or comments

 

[Deleted member 120897]

No harm in going for a Combi, the company I work for fit them all the time, and have converted many conventional systems, but I still think you’ll need flow and return pipes to all radiators. Leaks wouldn’t be the only pitfall, make sure you have the correct pressure, flow rate and hot water demand capabilities.

 

[Scott_D]

You could separate the boiler and system, keep
The system low pressure.

 

[Basher]

We have a large Victorian house with a one-pipe system. It works well in it's original configuration, now with a few rads added. I agree with scott_d!

Everyone seems to rubbish one-pipe, and wants to change to traditional flow/return, but you don't have to.
It's just a question of setting it up properly. We are lucky that the design of ours seems sound, with pipes sized appropriately, and valves in the various 'arms' of the system so different areas can be balanced. It's all in imperial copper, and probably 50 or so years old. I wouldn't dream of re-piping it.

We now have an Intergas system boiler, Y-plan, and Evohome TRV's in 10 rooms. It's still traditional vented, but plan to replace the cylinder with an unvented one - will still keep the rads low pressure.

Replacing the cylinder is a separate issue from whether it's worth the hassle of changing from one-pipe to two!
You could change to a vented, or preferably unvented, cylinder, independently of doing anything to the heating.
Ie leave the heating as is, if necessary with a new system boiler (if indeed you need a new one) and see how you get on.

PS There are Caleffi valves for one-pipe systems that can get you out of trouble if you have a problem in part of the circuit, but I haven't had to use one!

I don't know if the "gotta re-pipe a one-pipe" philosophy has come about through not understanding them, not having experience of them, or just trying to generate more work, but I vehemently encourage you not to change your system until it has been demonstrated as an insurmountable problem. One caveat though - if your system was designed for just 'background heating' rather than todays full central heating, it might need changes to up the output in the rooms. Possibly doable by upping the rad temps if that's an acceptable solution.

And smart controls do seem to help put the heat where it's needed!

 

[Matti5041]

We have a large Victorian house with a one-pipe system. It works well in it's original configuration, now with a few rads added. I agree with scott_d!

Everyone seems to rubbish one-pipe, and wants to change to traditional flow/return, but you don't have to.
It's just a question of setting it up properly. We are lucky that the design of ours seems sound, with pipes sized appropriately, and valves in the various 'arms' of the system so different areas can be balanced. It's all in imperial copper, and probably 50 or so years old. I wouldn't dream of re-piping it.

We now have an Intergas system boiler, Y-plan, and Evohome TRV's in 10 rooms. It's still traditional vented, but plan to replace the cylinder with an unvented one - will still keep the rads low pressure.

Replacing the cylinder is a separate issue from whether it's worth the hassle of changing from one-pipe to two!
You could change to a vented, or preferably unvented, cylinder, independently of doing anything to the heating.
Ie leave the heating as is, if necessary with a new system boiler (if indeed you need a new one) and see how you get on.

PS There are Caleffi valves for one-pipe systems that can get you out of trouble if you have a problem in part of the circuit, but I haven't had to use one!

I don't know if the "gotta re-pipe a one-pipe" philosophy has come about through not understanding them, not having experience of them, or just trying to generate more work, but I vehemently encourage you not to change your system until it has been demonstrated as an insurmountable problem. One caveat though - if your system was designed for just 'background heating' rather than todays full central heating, it might need changes to up the output in the rooms. Possibly doable by upping the rad temps if that's an acceptable solution.

And smart controls do seem to help put the heat where it's needed!

Hello thanks for that thorough response. Our system is part new in an extension built in the 1990’s then added to again about 5 years ago, the house itself was built in the 1960’s so the oldest pipe is that age at most. So the current system is designed to heat the rooms and it does to be fair. The radiators all get warm and we’ve replaced a couple of them with modern cast iron types with temp valves on, not had any issues.

 

[Basher]

Hello thanks for that thorough response. Our system is part new in an extension built in the 1990’s then added to again about 5 years ago, the house itself was built in the 1960’s so the oldest pipe is that age at most. So the current system is designed to heat the rooms and it does to be fair. The radiators all get warm and we’ve replaced a couple of them with modern cast iron types with temp valves on, not had any issues.

Thanks. It dosen't sound as if you need to do much, if anything, to the system 👍
Personally I wouldn't pressurise the radiators, but that's just me being cautious.