That will probably help but does of course mean that the water which was piping hot at the top is returned to the top slightly cooler, as a result of being circulated.

It did cross my mind but I'm trying to ignore that so please don't remind me 🤣  Hopefully the loss will be very small.  I will try it once the house if finished, but that is a long way off.

My ramblings about the shower valve being wifi connected - you made me think @johnnyb that it might be possible to install a switch either in a spare slot in my wall switch or a wireless switch that could tell a digital timer (rather than the mechancial timer I currently have) to swtich on or off. Would need one in my son's bathroom also. I'm not in any way electrical so not sure if that exists but my experience is that if you can imagine something wifi or smart, it probably exists.

That is what I was wondering about as well. My son's are old enough to think about switching the pump on if I make it simple for them and the water runs hotter.  Reading the first page I see that @ubert767 included a link to a switch at toolstation that does what we want, and if I understand it correctly there can be several switches connected to one receiver, so one in each bathroom shouldn't be a problem

https://www.toolstation.com/culina-single-kinetic-push-switch-kit/

Ah - you just hit on a problem - the boy has a switch in his bathroom for the recirc pump - on is no problem, but turning it off is another matter entirely. Motion sensors in the shower cubicle! 

Ah but you do pee with the light on (I assume) and I don't need the recirc pump when I'm peeing. Extractor fan might work yes unless its one of those humidity sensing ones. Of course all this falls apart when I try to tell my 10 year old to turn on an extra switch when he's showering - extractor fan, recirc pump, towel radiator...

Yes, this is how it works. As I mentioned above, our water is now heated to mid-40's and arrives at that temp at the shower head, where without the recirc pump we had to heat the water to the low or mid-50's (depending on time of year) and it would arrive more or less mid-40's at the shower head. So in my book that's a big saving on heating the water, plus the water saving of not waiting for the shower to heat up (100 litres or more per day). My current DHW usage grid consumption is around 5kwh per day; space heating is around 20-50kwh depending on solar and OAT, so comfort trumps other considerations for me. Don't judge.

I've just today started my trial though of heating the water to 58C at lunchtime (max solar) and hoping (well, AI calculated it for me) that it should be around mid-40's by 6am the next day, given evening usage for my son's shower and general domestic use; this should elminate my 5am DHW cycle which in the absence of solar and with the system being cool spikes at 6kwh.

My ramblings about the shower valve being wifi connected - you made me think @johnnyb that it might be possible to install a switch either in a spare slot in my wall switch or a wireless switch that could tell a digital timer (rather than the mechancial timer I currently have) to swtich on or off. Would need one in my son's bathroom also. I'm not in any way electrical so not sure if that exists but my experience is that if you can imagine something wifi or smart, it probably exists.

Good luck!

@jamespa our hot water flow and return pipe fittings are both at the top of the tank. Unless one has a pipe running down the inside of the tank I don't think there will be much mixing.  

Noted.  That will probably help but does of course mean that the water which was piping hot at the top is returned to the top slightly cooler, as a result of being circulated.

My understanding is if the pump isn't switched on we still get hot water the same as if there wasn't a pump but if it is switched on the hot water is there nearly instantly, there isn't a negative to having a pump as I can leave it switched off or just switch it on when needed

Thats my understanding also but someone reported otherwise, for reasons I haven't yet understood.  Try it and see, which doubtless you have already done!

My family are used to strange things with the hot water and having cool or cold showers occasionally when the DHW timings don't work if someone uses extra hot water. That's one of the main reasons for fitting a 300ltr tank, I expect to only heat the tank once a day when electric is cheap.

My understanding is if the pump isn't switched on we still get hot water the same as if there wasn't a pump but if it is switched on the hot water is there nearly instantly, there isn't a negative to having a pump as I can leave it switched off or just switch it on when needed. After reading this thread I am trying to work out if I can still get cables to the bathrooms to switch the pump on when we need a shower, or get a wireless switch/switches.

If I only switch the pump on for morning showers then I don't expect the heat loss to be too much higher. We currently have to run the shower for 30 seconds or so to get hot water and it cools down quite quickly so unless we shower immediatly after each other, which rarely happens, we are starting again. If I can have it so we switch the pump only when we are about to use the bathroom and only need to turn the shower on as we get in it there may not be too much difference and there will be less wasted water.

@jamespa our hot water flow and return pipe fittings are both at the top of the tank. Unless one has a pipe running down the inside of the tank I don't think there will be much mixing.  

New houses often have extra bathrooms/ensuites that older houses weren't designed with. Our main bathroom has the shower directly above the hot water tank and will have nearly instant hot water anyway but our ensuite is further away. I had mentioned waiting for hot water in our current house to the plumbers and they are fitting a pump without me even realising it was part of the quote.

@johnnyb Hopefully this will inform your decision.  @marzipan71 @jamespa have captured my issue in a nutshell.  Have the timer set for your "known" requirements in the mornings such as showers, washing up etc. And then just manually switch on as required for the rest of the day....my lot have got use to it....eventually.

Exactly, yes. Now if my shower valve was internet-connected, and I had a WiFi recirc pump switch on the DIN rail, I could have the recirc pump start and stop for those on-demand family showers. Our rain shower heads are 10 litres per minute so three showers a day are far and away the biggest consumers of hot water.

Better still if the pump had extra-sensory perception and could read your thoughts in advance so it could turn itself on at just about the right time.

Alternatively, just wait a minute for the water to come through!