Undersized heating pipes??

[Sweedo1982]

Hi guys, hope I can get some advice. I’m a gas safe engineer , working on a central heating issue, so I hope this in the the correct forum??

I was called to a job, where the customer has been having issues with the heating not working correctly and certain rooms not heating up. The customer asked me to powerflush the system and install an extra radiator in the kitchen. I did this , and when flushing the system. I noticed it was clean, and suspected another issue with the system. It was mainly a problem with the two radiators in the lounge on ground floor. I thought there could be a balancing issue, so closed all rads except for the lounge ones and still no heat would travel through. I suspected a blockage, so Took up carpet and assessed the pipework. It’s all done in plastic, and all in 15mm except for 1m of copper in 22mm from the boiler. The 15mm runs from boiler to landing upstairs feeds all upper rads , and drops down to the lounge rads. I am now suspecting that the pipework is undersized, but wanted to get some further advice before I commit to a re-pipe. Has anyone else had this issue before? I have seen systems pipes in 15mm before, and they worked ok, so any advice would be great. I have managed to drain the system and blow down the pipes on gomround floor , and there is no restrictions when system empty.

Regards James

 

[ShaunCorbs]

If you shut all the other rads off and they still didn’t heat not a loading issue was it grey plastic pipe ?

Also you had water out of each of the valves on the problem rads ?

 

[tamzbackforalook]

And why would grey pipe be an issue. Same stuff comes in grey or white. Colour is a personal preference.

 

[ShaunCorbs]

And why would grey pipe be an issue. Same stuff comes in grey or white. Colour is a personal preference.

Because it could be first gen plastic which doesn’t have an oxygen barrier so most of the time they clog up / block

 

[James c]

Hi guys, thanks for reply’s , it does start to heat when other rads are closed, but takes a very long time, and I can feel that it is not circulating.
Yes it is grey plastic pipe, system has been power flushed twice apparently, but I did notice that there is crud in the pipe work, when I cut and rejoined it was difficult to put liners in the pipe.

Could be looking at a repipe??

Thanks James

 

[ShaunCorbs]

If it doesn’t have an oxygen barrier tbh I would as it will only get worse

Eg this has a barrier eg the blue in the middle so if it’s just totally grey no split in the middle it’s the old stuff and best if you can replace

 

[John.g]

Hi guys, thanks for reply’s , it does start to heat when other rads are closed, but takes a very long time, and I can feel that it is not circulating.
Yes it is grey plastic pipe, system has been power flushed twice apparently, but I did notice that there is crud in the pipe work, when I cut and rejoined it was difficult to put liners in the pipe.

Could be looking at a repipe??

Thanks James

Is the boiler rapidly cycling on off with only these two rads on?
Is there a automatic bypass valve installed and if so its indexed setting?.

 

[Last Plumber]

15mm plastic pipe is only approx 11.5 mm inside diameter.

I wouldn't expect much more than 18000 - 20000 Btu/hr personally and it does depend on route, length and fittings/valves etc.

Look at the losses per meter on the tech site against your index circuit.

 

[John.g]

15m of 11.5mm ID will circulate 5 LPM to give a rad output of ~ 4kw at 1.2m pipe loss and assuming a dT of 12C , so total loss of say less than 2M allowing for rad valve losses etc.
Check pump head mode and setting.