Partial blockage in central heating pipe

[echoes]

Hello,

Conventional system, open vented CH and HW with 2 motorised valves.

My boiler overheats (the safety button pings out) when heating hot water only. I think this may be due to insufficient flow around a 15mm, sludged circuit.

I have a section of 15 mm copper pipe which carries the flow and return for the hot water cylinder. Firstly, I reckon this should be 22mm, but this is what is installed. There is a section of this pipe which is embedded in a solid floor in a U-shape. I can stick a magnet to this section of pipe indicating a local sludge build-up; the rest of the system seems OK.

I have tried mains flushing one radiator at a time, including the HW cylinder circuit, and this removed a lot of sludge, and there is now Fernox Heavy Duty restorer in the system which has been circulating for 1 week. The magnetic pipe seems slightly less magnetic, but there is clearly some sludge still in there.

I am reluctant to replace the pipe since it would involve replacing a laminate floor and much chiselling. Is there any other chemical cleanser I could used, or some mechanical unblocking method? I have relatively easy access to one end of the 'U'.

Any advice gratefully received!

 

[gas4you]

15mm pipe to hot water circuit was not uncommon, used to be used to help balance system by restricting flow!

From what you describe you need a proper powerflush machine used on the system. You can hire these or get a professional in to do the job!

 

[echoes]

Thanks Dave.

I think I'll hire a powerflusher then! Would they connect easily across a short, removed section of 15 mm copper (pump and boiler are in quite awkward positions)?

Richard

 

[Timmyturtle]

Pump the best place as most flow.
Will connect instead of a radiator though.

 

[Fluffster]

Richard
Make sure you read the instructions thoroughly and have a mate with you to do the running around opening and closing rad valves and also spotting any possible leaks.
Even after years of operating powerflush machines and a day training the process still likes to throw things back at me I have never experienced before.

Ensure the f/e tank is well capped/bunged off and keep checking during the process which should take about about 5 hours.
Pete

 

[ChrisR]

You might try a thin drain clearing spring. Wickes do 6mm diameter ones for a few pounds, 1.8m long.
If too many elbows, try a bowden cable from Halfords. Fold a piece double and put the cut ends in a drill chuck. Tape round if necessary. push the folded end into the pipe - it'll go.
Between the two is the spring they used to use - maybe still do, for net curtains etc. Strip the plastic sheath off.

 

[echoes]

Thanks for all the tips so far.... it's the first time I've used this forum and you've been very helpful.

Today I cut the pipes just before they go under the floor and used a net-curtain wire to loosen the sludge from both ends - there was a lot: 1-2 mm around the whole circumference of the pipe. I then connected two hoses to the open-ended cut pipes and flushed the offending section with mains water - much more sludge - until it ran clear. Repeated this several times. Also flushed the rads in turn while I was at it. Finished off by replacing 2 3-foot lengths of copper where I had cut, which was also sludged, but not as badly as the under-floor section.

Just refilled and bled, no leaks... HW and CH are on, fingers crossed!

If things don't improve then I'll powerflush. Does anyone recommend any particular chemical to use? I was thinking of using Fernox DS-40.

BTW, this CH system used to accumulate a lot of air and need frequent bleeding until I replaced the header tank (the old one had an inch of porridge at the bottom and the vent and feed shared a short section of 22mm pipe) and sorted out the vent and cold feed connections last year. I guess this was the root cause: many years of slowly-corroding rads! I no longer need to bleed the rads, but the sludge is a legacy.

 

[gas4you]

DS 40 is very good, perhaps too good in some cases If you use it read and follow instructions exactly. Also use a neutraliser afterwards

 

[echoes]

Thanks Dave.

I know it's strong stuff..... but what do you mean by 'too good'? Is it very good at finding leaky joints/valves or something?

Does it come with neutraliser, or should I buy this separately?

Richard

 

[gas4you]

Yes it will find any weaknesses rather well Fernox do a system neutraliser sold seperatley

 

[echoes]

Had HW only on this evening and no overheating boiler! Certainly a big improvement!

Many thanks folks!