Cold tap is warm when recirculating pump is on

[conny]

As Bod says, hot water at 60C-65C Cold water should be less than 20C after two minutes if tap used regularly.
Both temperatures allow legionella, and other bacteria, to be kept at bay.

Regarding the TMV's, we have had a similar problem in work where the cold temp of a morning, out of any one of about 120, is often as warm as 28C Investigations by an outside contractor, (approved and certified by the local water supplier), have so far discovered 3 TMV's that were installed back to front. i.e. the hot was fed to the cold inlet and cold to the hot inlet. Most probable cause was the valves were fitted with their markings towards the wall so weren't noticed when connecting up. The contractors also suspect we have heat transfer between pipes somewhere in the building. As this is a 4-storey building with about 300+ rooms/areas/toilets etc, there is a LOT of pipework to be systematically checked.

 

[phykell]

Hot water tank temperature | Vaillant

Find out more about your hot water tank and the ideal hot water tank temperature.

www.vaillant.co.uk

Thanks - that certainly sounds sensible but the temperature was configured by the Vaillant engineer who commissioned the system. I also picked up some advice on the Vaillant Arotherm Plus Facebook group:

Hot Water Temperature - Scalding and Legionella - HeatGeek

Among heating engineers, this is really going to ruffle some feathers. It's entirely possible to keep hot water permanently at 40°C, literally save 50% of

www.heatgeek.com

Half the problem with an ASHP is that the installers don't necessarily understand how to optimise a given setup and don't provide the end-user with the documentation/training necessary to effectively use the thing. My system has multiple zones each controlled by a thermostat but I'm told that I should have all of my valves open, thermostats disabled and that I should adjust my weather-compensated heat curve to control the heating, aiming for the lowest possible flow temperatue. Last bill I had was over £600 for the month using thermostats! As soon as the other issues are sorted, I'll have a go at optimising the system using just the heat curve variable.

 

[Deleted member 294929]

I don't know how that would stand up in court if the 1 in a million did happen.

 

[phykell]

Just to revisit the diagram again - the more I look at it the more I think that it's wrong:

The cold main is entering the group valve and the first thing is to regulate the pressure to match the cylinder.

The first takeoff from the valve is optional and can be used as a balanced output for the cold tap (to match the pressure of the hot of course). On my system, this first takeoff is what feeds the cold cylinder so it's bypassing the check valve built into the group valve.

Note that the built-in check valve sits between the optional balanced takeoff for the cold taps, and the takeoff for the expansion, pressure relief and the primary output of the valve, i.e. the output which should feed the cylinder as this feed is both pressure regulated and protected from backflow (via the check valve).

The pressure relief circuit is fine and routes to a tundish and then to the waste.

The primary output of the group valve feeds the cold tap in my system but it also links back to the cold cylinder input and thereby, back to the balanced output of the group valve - this is the section which oldbutnotdead noted was odd. Note also that the hot water return feeds back into the cold cylinder input as well, via a recirculation pump and check valve.

The installation engineer is booked in for tomorrow but I thought it worth adding the following images:

1. Current layout - modified to show a consistent view of the valves including the group valve.

2. My suggested alternative - routes the cold tap to the balanced output of the group valve and the primary output to the cold cylinder input and removes the odd link from the primary output back to the balanced output.

3. A picture of the actual group valve and labelled pipework.

 

[phykell]

Just to close this off, the engineer visited today and confirmed that there was an error in the installation: the pipework to the balanced takeoff should have been routed to the primary output (incorporating a check valve) and the pipework to the primary output should have been routed to the balanced takeoff. He came up with the same solution as I did - a check valve in the feed to the cylinder as an alternative to re-routing a load of pipework. Haven't tested thoroughly yet but it does seem like the cold taps I've tried are already noticeable colder.

Thanks everyone, for all the help

 

[gassymark]

Make sure you don’t put the check valve in between the cylinder and expansion it really needs to be re pipe correctly.

 

[phykell]

Make sure you don’t put the check valve in between the cylinder and expansion it really needs to be re pipe correctly.

Thanks - I did say this to them but I'm arranging a service of the system with the installers and will hopefully have everything resolved at that point. For now though, at least we haven't got warm water from the cylinder entering the cold water supply but I'm a bit concerned about the potential 4% water expansion.