Posted by: @transparent

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You shouldn't be getting a lukewarm bath if the tank temperature is 50°C.

When it is highlighted (selected, as it was in the image in the post), it is showing the set temperature, not the actual temperature. It shows the actual temperature when it is not highlighted.

@cathyem1 - assuming the default DHW heating comes on when DHW falls five degrees below the set DHW temp, and a set DHW temp of 50, what you are looking for is a rise in the actual DHW temperature when it falls below 45 degrees back up to 50 degrees. Have a look at it every now and then, and see if you can see that pattern of behaviour.

Or just wait until your supplier turns up tomorrow!

@cathoderay thank you. Very interesting that the temperature it is showing when not highlighted is the actual temp.

I have just had a lovely hot bath and the temp is now showing at 13°. 

Posted by: @cathyem1

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I have just had a lovely hot bath and the temp is now showing at 13°. 

Excellent (the hot bath)! Since the actual temp is now way below the 50 degree set temp, it should switch to DHW heating mode and get back to 50 degrees. When it is not on a timer, the DHW priority (over space heating) should mean that whenever the tank is five of more degrees below the set temp, it goes into DHW heating mode. Have another look in ah hour and see what it shows then.   

@cathoderay Our 01.00 to 06.00 electricity tariff is going to be 5p kWh. Is it possible to set the DHW to heat overnight?

Posted by: @cathyem1

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Our 01.00 to 06.00 electricity tariff is going to be 5p kWh. Is it possible to set the DHW to heat overnight?

Yes, but first of all we need to know the DHW heating is working. Did the actual DHW temperature rise after it went down to 13 degrees yesterday after your bath?

[aside] I'm impressed how much @cathyem1 is picking up from this discussion and diagnosing what's going on. 🤗 

This is just the sort of background knowledge which needs to spread across the rest of the population.

I hope the meeting with the installer goes well today.
Please let him/her know of this topic.

@transparent It did go well! The timer has been set for our DHW to heat in our 5p kWh window overnight and he’s brought our flow rate down to 40°. He was slightly pursed-lipped when I asked and did say the parts of the control panel that do that aren’t really for the customer - read Muggle 😉

I'd already found the pass code and guidance for changing the heat flow on the CP via Youtube - so I told him the code 🫢

Anyway, upwards and onwards. Hopefully we’ll feel just as snug tonight for less money 💵 

@cathoderay You’re on fire!! The installers had put the temperature sensor into the wrong pocket on the cylinder, so the heat pump was permanently trying to heat the DHW. Explains why I kept having to override the system to warm the house 😉

@cathyem1 - 2 3 4 and through the door...

Posted by: @cathyem1

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The installers had put the temperature sensor into the wrong pocket on the cylinder,

I had that thought and then discounted it on the grounds they couldn't be that dumb. The sad lesson is never under-estimate how dumb 'the professionals' can be. Harsh, but true.

Posted by: @cathyem1

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he’s brought our flow rate down to 40°. He was slightly pursed-lipped when I asked and did say the parts of the control panel that do that aren’t really for the customer

'aren't really for the customer'??? Whose heat pump is it anyway? I think it may be that he has left the system on a fixed flow temp (not rate, rate is the amount of water over time, not its temperature, though both matter) of 40 degrees, which means it is still not on weather compensation. The 'at a glance' way to tell is by what you can see on the left hand heating side panel on the wired controller if you select the big number in the middle there and use the up or down arrow to try to change it. If the display then says 'Weather temp set function is on. Do you want to turn it off?' then you are using weather compensation (so back out without changing anything). If you can change it, then you are not using weather compensation.  

@cathoderay It looks like we are using weather compensation!!!

Apologies for not addressing this earlier

The Red knob is an over-temperature/pressure relief valve.

In the event of a fault, it will allow the scalding hot water to be discharged rapidly into the tundish below it,
and then routed to the outside via the larger pipe connected at the outlet.

... except that the tundish and safety pipe aren't present.

So in the case of @cathyem1 's installation, the pressure will build up until it overcomes the friction of the rubber o-ring in the white end-cap.
That projectile will be propelled into the insulation of the pipe below it...

Fortunately, the noise should be sufficient to wake up the household. 😯 

@transparent Yikes! I wish I'd known that when the chap was here, but thank you for bringing it to my attention.