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I have a large 2 story house with a single-story flat at the side. The flat has a kitchen on the ground floor and en-suite in roof space. The house and flat are both serviced by a boiler and hot water storage tank in the laundry room on the ground floor of the main house. It takes a minute for hot water to arrive at the water outlets in the main house and a lot longer in the flat. The water supply ( hot and cold ) is pressurised.
I have made provision for secondary recirculation loop in the main house but have not connected in up yet and have not purchased a recirculation pump. I have been told that the Grundfos Comfort Autodapt recirculation pump doe not have sufficient Head as the max head is 1.5 m. Grundfos has suggested 5m head would be necessary. Is there other recirculation pumps with a higher head with the auto adapt feature.

I could use 5m recirculation pump with from Grundfos but this would require to be on continuously or on a fixed timer all of which is wasteful of heat and electrical energy.

Another option I have been considering is to have a 2nd small well insulated unvented tank in the house roof space. A recirculation pump would transfer hot water from the main tank when the temp in the secondary tank dropped below a certain level. The secondary tank would be sized to hold about 5mins of water. Hot water would be available more quickly as the pipes from the secondary tank would be shorter.

I would appreciate any comments you might have on the feasibly of the above arrangement.
Also some advice on hardware; unvented tank, recirculation pump, temperature sensor.

The advantages of this option are:

Small amounts hot water in available quickly at kitchen and bathroom sinks.
The secondary tank need only be recharged as hot water is used when the temp in the secondary tank falls.
The problem of hot water delay in both flat and house is resolved as both house and flat hot water flow through secondary tank.

Catch 22 with a larger property. We have had it in the past when fitting a pump on a loop so you have instant hot water at a tap on a long run, not very efficient. If its a large building & quite a few living there or a hotel/guest house, its needed. But what we found is the circulating pump was dragging the heat away from the hot water tank & the boiler was firing up more often. so not very green. Have you thought about instant under sink hot water heater for a local hot water.??

I have kitchen sink , bathroom sink and shower that needs to be supplied with hot water. I thought that by using 2nd well insulated hot water tank with thermostat controlling recirculation pump that the 2nd tank would only be charged 1-2 times a day. Pipes from the 2nd tank would be shorter and hot water would appear at outlets quicker.

If you was thinking of a second tank, why not treat the system as a 3 zone & have a programmer that has three timers. H/HW/HW

Hi, Can you please elaborate on the 3 Zone solution you suggested.

Not sure on what set up you have, but in many large house you would have "Lets say" one flow from the boiler to 3 x 2 port motorized valves. One for hot-water, one for downstairs heating & one for upstairs heating, then 3 returns back to the boiler. You would have the same, but one for heating & the other two for the hot water tanks. You would then need an extra time switch & cylinder stat. Or change your programmer for a 3 way [url]https://www.amazon.co.uk/Horstmann-H37XL-Channelplus-Electronic-Programmer/dp/B002NAGI2E/ref=asc_df_B002NAGI2E/?tag=googshopuk-21&linkCode=df0&hvadid=231982504303&hvpos=1o3&hvnetw=g&hvrand=11554847306767693133&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9044869&hvtargid=pla-420297065190&psc=1[/url]

[img]https://i.postimg.cc/KvhwHmXz/boiler.jpg[/img]