Plumbing in a de-strat pump.

[Stevex]

Hi, first post here and am after some advice please.
I'm having solar panels fitted in the next few weeks and the fit will include an iboost+ to use the immersion element to generate hot water.
I've checked the immersion and using a couple of heat sensors it's apparent the element only heats the top half of the tank, which normally generates hot water via a gas boiler.
My plan is to fit a de strat pump so that the solar energy will provide a full tank of hot water.
The pump has an NRV and a Stop valve built in and also has an integral timer.
The attached picture is a simplified diagram of my vented system hot and cold water pipes. The cold feed comes from the header tank in the loft and the head of the cold water feed is approx 3-4 feet above the top of the hot water tank.
The copper pipes in the diagram are only accessible above the top of the tank.
I know the connecting pipe with the pump attached needs to go from the hot water pipe to the cold feed.
Can I fit the T piece above the joint on the right hot water supply pipe? The vent pipe will have a good few feet of water in it before the vent goes above the header tank water level.
If I then take the pump straight across to the cold feed pipe and connect it via another T piece, will this provide adequate circulation of the hot tank water?
Is there any possibility that cold feed water will be drawn from the header tank when the pump is running?
Have I missed anything?
Thanks.

 

[ShaunCorbs]

Nrv where the red line is on both pipes eg black line and cold feed

 

[Knappers]

I don't think it would be good practice.
Not only would you risk dragging air into pump when pump and outlets are running but you should maintain a 400/450mm ( can't remember) horizontal run on cylinder outlet partly to avoid convection in pipework from heating vent.
Could consider somewhere close to cylinder outlet or pos on shower feed?

 

[Stevex]

Nrv where the red line is on both pipes eg black line and cold feed

Problem is there is no room below the top of the tank, its in a very narrow airing cupboard. Also, the cold feed goes down the back wall of the cupboard and ibto the back of the tank, no space or access.

 

[ShaunCorbs]

Where is the tank located eg is there a wardrobe or somewhere that doesn’t mind an access hatch ?

 

[Stevex]

The attached picture is a better representation of the shower pipe t-off position. I could get another t piece at the blue line and attach it 6 inches below the top of the tank on the cold feed. That is as good as it will get access wise. The only access to the back of the cupboard would be thro' the bathroom, but all that rooms walls are fully tiled.

 

[ShaunCorbs]

that’s fine but you would mostly need around 12” as you have valves and check / nrv s

 

[Stevex]

Knappers,
above new picture is the best I can do access wise. The point you make about a 400mm run and convection; all I can say is that I plumbed the shower feed in many years ago and it supplies a pump under the bath prior to a thermostatic mixer and it's always performed really well, no cavitation or other problems. Would the blue line lay out above be much different?

 

[Stevex]

 

[ShaunCorbs]

You will require valves on the pump and a nrv on the cold feed

 

[Stevex]

You will require valves on the pump and a nrv on the cold feed

OK, I take it the NRV is fitted to prevent the cold tank from back filling, that could go on the cold feed pipe above the T piece?

 

[ShaunCorbs]

Correct