Newark ministore DHW cylinder (Shell and Tube Heat Exchanger)

[Tide2]

Has anyone experience using or installing these with a gas combi boiler

[JohnMo]

2 hours ago, Tide2 said:

Has anyone experience using or installing these with a gas combi boiler

Why would you install with a gas combi? Tell us what you are trying to achieve?

[Nickfromwales]

1 hour ago, JohnMo said:

Why would you install with a gas combi? Tell us what you are trying to achieve?

Usually to get higher DHW flow rates, or possibly somewhere to bin off some excess solar PV.

[JohnMo]

28 minutes ago, Nickfromwales said:

Usually to get higher DHW flow rates, or possibly somewhere to bin off some excess solar PV.

Maybe simpler to do it upstream of the combi rather than after. Then small amounts of temp rise give massive uplift in flow rate.

 

Combi-SuperFlow-White-Paper-v1-2-4.pdfCanetis-SuperFlow-Product-Sheet-WE-050318.pdf

 

You can also do it way more cheaply than a mini store. As a mini store is based on heating medium in the cylinder and domestic water in the tubes.

 

So you really need to connect the combi to system boiler for the proposed to work.

[Nickfromwales]

21 hours ago, JohnMo said:

Maybe simpler to do it upstream of the combi rather than after. Then small amounts of temp rise give massive uplift in flow rate.

 

Combi-SuperFlow-White-Paper-v1-2-4.pdf 960.61 kB · 12 downloads Canetis-SuperFlow-Product-Sheet-WE-050318.pdf 322.43 kB · 5 downloads

 

You can also do it way more cheaply than a mini store. As a mini store is based on heating medium in the cylinder and domestic water in the tubes.

 

So you really need to connect the combi to system boiler for the proposed to work.

You’re still always constrained by the physical max flow rate of water, whatever temp, through a combi.

[JohnMo]

49 minutes ago, Nickfromwales said:

You’re still always constrained by the physical max flow rate of water, whatever temp, through a combi.

Could get 3 showers out of mine, you take the flow restrictor out, I never installed mine, because I always preheat with upstream preheat, can't do any better with UVC I now have. 

Edited Monday at 17:41 by JohnMo

[Nickfromwales]

5 hours ago, JohnMo said:

Could get 3 showers out of mine, you take the flow restrictor out, I never installed mine, because I always preheat with upstream preheat, can't do any better with UVC I now have. 

UVC doesn't give higher flow rates at the 50^o+ temps? Combi's can't usually be compared.

 

3 showers is very good, at what flow rates?

[Tide2]

On 21/12/2025 at 17:36, JohnMo said:

Why would you install with a gas combi? Tell us what you are trying to achieve?

I want to use solar PV for hot water during the summer months. Also, the cylinder could be sited nearer the main drawoff points, thus avoiding the annoying wait for the water to run hot. I believe this will reduce energy costs, with a modest outlay, with a fairly simple system

[JohnMo]

21 minutes ago, Tide2 said:

modest outlay,

£1400 isn't modest in my book. Plus if used the way you are suggesting you would need a full safety group.

 

You may have a few things to resolve. If water flows through the combi it will fire up, so use gas anyway. If heat store isn't heated, sun not playing ball, it would just cool the water already heated by gas boiler. So no hot water!

 

I would install cylinder upstream of the combi, heat by solar, if water is above 45 divert around boiler direct to tap, if below 45 let it be heated by boiler. Saves boiling firing when not needed etc.

[Tide2]

29 minutes ago, JohnMo said:

£1400 isn't modest in my book. Plus if used the way you are suggesting you would need a full safety group.

 

You may have a few things to resolve. If water flows through the combi it will fire up, so use gas anyway. If heat store isn't heated, sun not playing ball, it would just cool the water already heated by gas boiler. So no hot water!

 

I would install cylinder upstream of the combi, heat by solar, if water is above 45 divert around boiler direct to tap, if below 45 let it be heated by boiler. Saves boiling firing when not needed etc.

Thanks for the reply

 

"£1400 isn't modest in my book."

*Agreed, it's modest compared to a heat pump and solar PV system though

 

"Plus if used the way you are suggesting you would need a full safety group"

Not familiar with this term, could you expand please

 

"You may have a few things to resolve" 

Not sure I follow your logic in this paragraph

The cylinder is heated from the heating side of the combi Via a 2 port valve controlled by a cylinder stat. A second 2 port valve valve would be required to allow heating via a room Stat. all this adds complication of course. The hot water side of the combi is not used. The DHW draw is via the the heat exchanger one side being mains fed the other to the taps, as there is very little stored water to be heated in the heat exchanger, way under 15L, so no tundish or discharge pipework required 

I do like your preheat cylinder idea, not sure it would help with the long draw off time though

[JohnMo]

If you have the space put a proper UVC in.  The mini store is unlikely to perform much better than your combi except immediate draw of would be quicker.

[Tide2]

9 minutes ago, JohnMo said:

If you have the space put a proper UVC in.  The mini store is unlikely to perform much better than your combi except immediate draw of would be quicker.

I dont like the added complication of the tundish and discharge pipe work in my situation 

Thanks for your input

[Nickfromwales]

22 minutes ago, Tide2 said:

I dont like the added complication of the tundish and discharge pipe work in my situation 

Thanks for your input

You won't have a choice, if you put an immersion heater into a sealed system.

[Tide2]

Thanks for pointing that out. There was no mention of it in the info I looked at, but I did have a concern at the time. Thinking about it, how is it different from the combi input heat, which would be far greater

Edited 3 hours ago by Tide2

[Nickfromwales]

7 minutes ago, Tide2 said:

Thanks for pointing that out. There was no mention of it in the info I looked at, but I did have a concern. Thinking about it how is it different to the combi input which would be far greater

The combi is full of weak components and no cylinder, ergo something would just go pop if it ever super-heated the water. Loads of failsafe avenues there.

 

If you heat a sealed cylinder, it becomes a bomb.