Central Heating Circulation Problem - Single Pipe System

[Jeevan]

Hello,

I’ve moved into a property with a conventional 6-year-old Vaillant boiler with water tanks and a single pipe system. Initially the downstairs radiators wouldn’t heat up. After having new lock shields and TRVs fitted, system power flushed and new pump installed, all radiators heat up but downstairs not as hot as upstairs.

On Central Heating only function the temperature on the boiler rises very quickly and it switches out, as temperature drops it switches back in again. When hot water and heating are both on, this is less of an issue. Been advised it’s a circulation problem and boiler display indicates this.

Is it advisable to get the existing pipework replaced with combi boiler and two-pipe system? Dilemma is that I’m having flooring replaced so it’s an opportunity to get pipework upgraded while flooring is up. However existing system still does the job despite issues outlined. Would really appreciate some advice.

Cheers

 

[Aire]

One pipe systems are outdated. If you've got the opportunity to replace it for a 2 pipe then do it. The boiler won't need replacing but if you want a combi and your house is suited to it then go for it.

 

[Gasmk1]

have you fitted correct TRV's ones that can be fitted on a one pipe system

 

[Simon Blackburn]

I did masses of research when fitting a new (extra) radiator to my single pipe system and got the balancing right. The only valves that I read worked are Danfoss RA-G-15s with RLV-S Lockshields. That (with a brand new radiator) was incredibly successful, even having two elbows in the flow and return from the single pipe to take it through the wall.

It now puts the other radiators with 1960s valves to shame... problem is I don’t have £70 per valve set (yes, they really are that expensive) to do the others! I can recommend those parts as fit for purpose though.

 

[SimonG]

're pipe

 

[SJB060685]

One pipe systems are technology from quite literally decades ago. You should replace to get things up to a modern standard. Naturally with one pipe systems the rads first off the circuit will heat up before the last.

 

[Chuck]

Just my opinion but...

One-pipe systems just need too much TLC to keep working, as you're discovering. I'd re-pipe and convert to a closed (pressurised) system. As a second priority, if the money is available, I'd change the DHW cylinder to unvented and get rid of the the tanks in the roof. I would not replace a stored DHW system with a combi without a very compelling reason. I would expect a six-year old Vaillant to have quite a lot of life in it so replacing it would not be a priority for me.

 

[SJB060685]

I agree with chuck. A combi will work fine for the right house and the right DHW needs but personally I always suggested an unvented cylinder. There’s pros and cons to both but if you’re seriously thinking of upgrading I would at least consider what we have suggested.

 

[Jeevan]

Just my opinion but...

One-pipe systems just need too much TLC to keep working, as you're discovering. I'd re-pipe and convert to a closed (pressurised) system. As a second priority, if the money is available, I'd change the DHW cylinder to unvented and get rid of the the tanks in the roof. I would not replace a stored DHW system with a combi without a very compelling reason. I would expect a six-year old Vaillant to have quite a lot of life in it so replacing it would not be a priority for me.

Thank you Chuck. You've also answered my next question regarding whether to replace the boiler. I'll stick with the existing one as advised.

 

[Knappers]

One pipe systems are often misunderstood, repiping is probably the best route unless you can find a proper old-school heating engineer.