Hi @toodles That external insulation looks pretty poor to me, but not unlike my original insulation. Cable ties are definitely not to be recommended. I would recommend Dave Smith's products - see https://primary-pro.co.uk

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He is very helpful and his insulation solutions make a lot of sense.

@mike-h Thanks Mike. Toodles.

@toodles An interesting question so I did some research. An uninsulated 28mm pipe with a 55C difference between the water temperature and ambient will lose 76W/m. Insulating that with 1 inch foam will take that down to 10W/m i.e. 0.1 W/cm. Assume that compression doubles the losses to 0.2 W/cm and that each compromised section is 2 cm then the additional loss is 0.2 W per zip-tie. Assume 300 hrs per annum where the outside temperature is around 0 C then you get 60 Wh per zip-tie per annum, slightly under 2p. [someone might like to check my figures!]. On the other hand sections of bare pipe will be losing heat at nearly 8 times that rate and may be much longer. My external pipe runs look like the ones in Mike H's photo but I'll be been checking out the joints and exposed fittings in my garage just in case ..

There are many assumptions in this and I would imagine that the zip-ties don't destroy the insulation, merely move it around so the insulation will still be there, just moved to the adjacent bits of pipe. 

@dr_dongle From your figures, this suggests the heat loss is undesirable but fairly insignificant. As to moving the insulation around, I’m not so sure as the overall diameter on either side of the tie does not increase in my experience, it is just that it is compressed where the tie applies pressure. I have now had the ties removed and the crushed sections have all been replaced with new; the replacement ties have been placed on top of adhesive ‘straps’ which spread the load and the ties are minimal tightness to perform the job. The vertical pipework no longer has any ties as the electrical ‘hose’ has been retained in a different fashion now. Regards, Toodles.

@toodles undesirable but insignificant sums it up pretty well though the cumulative effect may be another matter.  I have a retro-fitted hybrid system here so I have two lots of everything with valves to separate them so I tallied 70 zip-ties (20 in the garage where temperatures can plummet), two pumps with shut-off valves, two filters ditto, three other pairs of shutoff valves, two air bleed valves, two drain points and four large compression fittings at the buffer tank. That is all in the plant room and some of that is in the return but it is all exposed brass and it all adds up. It was an interesting exercise and I'll do the calculation properly when I have a minute. 76 W/m on exposed copper is quite a thought ..

@dr_dongle Even at ‘insignificant’ levels, all those ties certainly add up! As best as I can see, no insulation has been squashed, squeezed or crimped on my system now; once those external pipe runs I photographed enter the brickwork, they are in the airing cupboard and there, the hot runs are insulated cleanly too. Regards, Toodles.

@toodles Sounds like you're sorted - these things niggle though once you spot them.  I totted up the bare metal on the flow side of my system and I came up with just over a metre so on the coldest night in theory that could be 80 watts - unlikely for lots of reasons and it would provide some frost protection but it was an interesting calculation. The biggest single items were the pump with its isolating valves and a motorised valve.

@dr_dongle I saw a YouTube presentation from one of insulation makers; they showed how to create bespoke covers around pumps and various valve devices, very neat if fiddly to create! Regards, Toodles.