Buffer Tank Hot when Heating Mode Turned Off

[James1234]

Hello all, moved into our extended/refurbished house a couple of months ago. We have ASHP (Daikin unit), hot water cylinder and buffer tank. The space heating has 4 zones in the house (upstairs/downstairs, old house/extension).

 

The system was designed by the Daikin rep at the local plumbers merchants, install by local plumber and signed off by separate MCS certifying company. I am not 100% convinced that everyone in that chain has done what they are supposed to as when I quiz one they refer to the others. If I was doing this again I think I would have taken a different route.

 

We are getting hot water and in the colder months heating was working fine. Now we are into summer I have put the master controller into 'heating off' mode. My understanding was the buffer tank was just associated with the space heating and would therefore be cold when the space heating was off, but it has remained hot. I quizzed the plumber who installed everything it who says that the buffer tank is used when the DHW tank had got up to temperature to allow the ASHP unit to wind down, as it couldn't turn off straight away. Seems wildly inefficient to have a tank of hot water sitting there for 6 months of the year.

 

Interested in other people's thoughts and suggestions.

 

Plumbing drawing and photo of installed system below.

 

 

 

Many thanks.

 

James

 

 

 

[SteamyTea]

Your 'buffer' looks more like a volumiser, if it is getting warm when heating is off, but DHW on, then there must be a path if least resistance through it.

Are the pipes to the UFH manifolds also getting warm?

[IGP]

1 minute ago, SteamyTea said:

Your 'buffer' looks more like a volumiser, if it is getting warm when heating is off, but DHW on, then there must be a path if least resistance through it.

Are the pipes to the UFH manifolds also getting warm?

Looks like a buffer, the drawing suggests a volumiser but the photo looks like it has four ports being used. 
 

Looks like it could do with the buffer being removed (or at least bypassed with the aid of a bit of piping and valves). Also sounds like it’s over zoned and can see third party controls which generally mean weather compensation isn’t been used. Could be wrong but it looks like it’s been setup very boiler-esque. 

[Nickfromwales]

Needs more questions asked, and some clarity on plumbing arrangements, but I think it simply needs a 2-port zone valve on the return to stop convection heating from the cylinder. 
 

It’s defo a buffer as it’s piped up as a 4-port setup.

 

My guess is that heating flows through the buffer by design, when heating mode is selected, as does DHW primary flow. The thing I can’t see is the 3-port diverted valve that sends flow to each discipline individually.

 

Can we have some better pics plz, show plumbing from different angles, all valves etc, insulation removed wherever possible?

 

What temp is the buffer sat at when only DHW is on?

 

Do you turn heating off on the ASHP control as well as on the 3rd party heating controls of the UFH setup? 

[SteamyTea]

28 minutes ago, IGP said:

Looks like a buffer

Didn't look at the picture.

Seems to have at least 3 pipes connect, so yes, a buffer.

 

Need some insulation on the pipes.

Get the installers back and get them to correct it to the drawing.

[James1234]

Pipework to the manifolds is not getting hot, just the buffer tank itself.

[Nickfromwales]

1 minute ago, James1234 said:

Pipework to the manifolds is not getting hot, just the buffer tank itself.

 

6 minutes ago, Nickfromwales said:

Do you turn heating off on the ASHP control as well as on the 3rd party heating controls of the UFH setup? 

?

 

Are you telling the heat pump itself that heating is off? 

[James1234]

4 minutes ago, SteamyTea said:

Didn't look at the picture.

Seems to have at least 3 pipes connect, so yes, a buffer.

 

Need some insulation on the pipes.

Get the installers back and get them to correct it to the drawing.

So would you say the drawing is a correct/proper setup? But the plumber hasn't installed what has been designed?

[James1234]

7 minutes ago, Nickfromwales said:

Needs more questions asked, and some clarity on plumbing arrangements, but I think it simply needs a 2-port zone valve on the return to stop convection heating from the cylinder. 
 

It’s defo a buffer as it’s piped up as a 4-port setup.

 

My guess is that heating flows through the buffer by design, when heating mode is selected, as does DHW primary flow. The thing I can’t see is the 3-port diverted valve that sends flow to each discipline individually.

 

Can we have some better pics plz, show plumbing from different angles, all valves etc, insulation removed wherever possible?

 

What temp is the buffer sat at when only DHW is on?

 

Do you turn heating off on the ASHP control as well as on the 3rd party heating controls of the UFH setup? 

Will get some more photos when back home this evening.

 

Heating is turned off at the 4 thermostats and also selected on the black controller which I am told talks to the ASHP (you can select to turn off the DHW tank, set times that the DHW is heated to suit lower electricity prices etc.

[SteamyTea]

36 minutes ago, James1234 said:

would you say the drawing is a correct/proper setup

Well it is a setup.

As @Nickfromwales points out, probably needs some isolation on the heating return.

 

 

[James1234]

Thank you all for your help on this, it is really appreciated, as is the wider Buildhub, I have used it a lot for ideas, guidance and support during my build. 

 

Sorry to take a while to reply, I was keen on getting the best photos and making them up clearly to make things as simple as possible. Below are a set of marked up photos showing closer up images of the system (one which shows before the insulation and solar inverter went in). The temperature of the buffer tank is over 42 degrees (my Boots thermometer stopped working at that point because it thought the patient was suffering sever heat stroke).

 

[JohnMo]

On 25/05/2025 at 15:16, James1234 said:

We have ASHP (Daikin unit), hot water cylinder and buffer tank. The space heating has 4 zones in the house

For me would look to eliminate the buffer all together and move the heating to a single zone. You have so many pumps, all need power and will eat through electric.

 

If you can eliminate all the zones and run out loop.

1. Heat pump will just supply the UFH directly no pumps or mixers needed. Good chance you can run the whole system cooler, as no mixing will occur. So you get a better CoP. You run cooler, because mixers are gone and without buffer mixing in there doesn't occur either.

2. You eliminate at least 2 pumps. They will pull approx 60W each, run most of the time over the heating season, so 0.060Wx2(pumps)x24 (hrs)x180(days)x£0.25 is £130 cost savings a year for pumps alone. 

3. You will have to do some loop tuning to get system balanced.

 

but could save around £200 per year overall

 

Things you need to sort out. 

External insulation where you enter the ground. Then Seal the conduit end before you get mice living there.

 

The ideal place for your controller isn't where it is, it should be in your hallway or somewhere that represents house temperature.

 

Insulation needed on hot water circulation from cylinder. Look to add 25mm wall thickness insulation to those pipes. I would look to add a timer to the pump also if one not there already.

 

In fact whole cylinder pipes insulation.