Posted by: @jamespa

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@bazcurtis 

 

Why not do a DHW run and then turn heating off.  Make sure that the circulation has stopped.  That will tell you whether its the valve or not.

Thanks for the idea. Isn't that what happens at 3pm? For us, once the heating goes off at 9am, it very rarely comes back on until 4pm on cold days. If it does, it goes off at 7pm. This is when the DHW seems to cool fast (when it does it). This is a 7pm example from February. You can see the heating go off. I wasn't monitoring the outside temperature at this point.

From what everyone is saying, it would most likely be the 3 way valve in the cupboard next to the tank?

@bazcurtis Mine seemed to be permanent but it's hard to say really - the trigger was that I was losing heat far too quickly. My thermal store is 500 litres, and I run two DHW cycles per day. The first cycle is 5am, and to be fair we take two 10 l/ minute showers around 7am, so I figured it was reasonable that the water was barely warm by mid morning. The second cycle is at lunchtime, and I noticed that by late afternoon the DHW was lukewarm, and the wasn't enough hot water for my sons shower after sports around early evening. I can't say it was every day but it seemed like that. AI (Gemini) diagnosed as per above. With the new valve I've noticed the hot water is noticeably hot throughout the day, and as above the recirc pump behaviour has changed, so there must have been something wrong with the valve. Yours being linked to OAT seems to be different to my problems, but it wasn't something I considered TBH. Your problem might not have anything to do with the valve/ actuator but I shared just because the rapid loss of hot water seemed similar behaviour.

@bazcurtis you would look to see if there is an additional pump gold or yellow colour normally piped in on the cold water inlet or at the top of the tank, its the pump that sends the heated water around the property so you can access DHW instantly rather than wait 30s - 1m, its hard to detail as some tanks are different, the post you added below they speak about it too:

Exert below: 

One curious thing - I have a recirc pump on the DHW pipe. Previously, when it turned on the effect was literally instant. However, with the new valve installed there is a small delay of maybe 30 seconds before the hot water arrives (without the recirc pump, it's minutes)

@ashp-bobba I don't think we do. We have to wait for the hot water, but no longer than gas.

@bazcurtis Ok, that rules that out then, sometimes if the secondary pump line is not insulated it can register the same losses like you show on the graph. I think the other advice is looking likely and check the diverter is locating correctly.

@ashp-bobba Looking at the arrow on the front it seems to close all the way and I can't turn any further to the left, which I believe it closed.

Posted by: @bazcurtis

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Looking at the arrow on the front it seems to close all the way and I can't turn any further to the left, which I believe it closed.

To rule it out arrange for a DHW reheat and then the heating to be switched off immediately afterwards for a few hours (check the circulator pump isnt running).  If the DHW tank doesn't cool then it probably is the 3 way valve, if it does cool then it definitely isnt the 3 way valve.

@jamespa That for the advice. This is normal how the house heats anyway. Once the house is warm enough the heating rarely comes on after the mid afternoon hot water top up. Now the heating is never on, yet yesterday and today the water immediately cooled after the water had been heat around 4.45am. In fact this morning it was above 40c until just after 3am. Then the heat pump came on for a very short period of time and then the heat loss kicked in until it was meant to heat the water. It then lost temperature again.

The heating is set to come on at 5am at 20c. It never needed to kick in so it is only doing hot water now.

OK.  If the cooling only occurs when the heat pump is doing space heating and doesn't occur when it's not doing space heating then the most likely explanation is the diverter valve.  Either fully or partially stuck, incorrectly wired (in which case the problem would have occurred from when installed) or incorrect valve (3 way instead of diverter - in this case also problem would have occured from when first installed) or loose cinnection  Very unlikely but not impossible is a controller fault.

Hopefully that gives you enough info to work it out.

You could try manually operating the valve using the lever on the side, this may free it if it's stuck.  Otherwise you need it fixed.  Any plumber should be able to do (but  make sure they know it's supposed to be a diverter valve not 3 way it unless it's a controller problem, it's a pig of a job if it's the actual valve, fairly easy if it's the solenoid that drives the valve.  The latter is more probably but the former can't be ruled out.

One final possibility is that it's 2 on off valves and one has failed.  Relatively unlikely but again not impossible

@jamespa Thanks for the information. The heat pump was installed in July so it may have been less noticeable

It is only the last few nights that I have seen it do when the heat pump is not running or even been running. The image below from the 20th seems to be very strange. The water temperature was fine, the heat pump came on around 70 seconds are 3am for what seems no reason. The tank temperature started to drop right after that. It is a zoomed in version of the above.

Of course it did not do it last night at all. Are you talking about this valve?

Posted by: @bazcurtis

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Of course it did not do it last night at all. Are you talking about this valve?

I would think so although the marking doesn't make sense.  Has it got a part number on it, are there any similar looking valves

Edit. Google lens says it's a constant flow temperature control valve.  If it's right then  not this valve and no idea what this valve is doing!  Hunt around for other valves.  Do you have ufh?

@jamespa Sorry, I don't know what a UFH is. That valve is the one that switches from hot water heating back to the house heating. It is the valve showing in the top of the screenshots. It is "off" most of the time.