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Hi

I have an Ecodan QUHZ-W40VA with a thermal store. After much technical assistance from Mitsuibishi, some installation tweaks and fine tuning by me, the system o/a is performing well. The COP is acceptable, the running costs are low and generally I’d say setup suits the house.

Like other heat pumps, mine prioritises DHW. It’s programmed to heat the water once each day. The problem is that I have an experienced a delay before the the heat pump fires up after DHW cycles?

The DHW (in my case the water in the store) is usually heated to around 50C. but the HP won’t re-start until the residual heat in the system (according to the thermistors) has dropped to match the heat flow temperature. For example if the flow heat temperature is say 30C or less, the cooling can take a very long time. It’s less a problem when it’s very cold, and more so in the shoulder seasons. 

Has any one else experienced this? Mitsi say it’s just not a problem and all is working as it should be.

Hey @Barry the bear 

 

Welcome to the Forum.

 

It doesn’t look like we’ve got any other topics specific to delays prior to the heat pump kicking into the DHW cycles, but there are lots of other topics on hot water control and other Ecodan/DHW related queries that may still be helpful:

 

 

Glad you’ve already reached out to Mitsubishi about it, shame they couldn’t clarify it a bit more.🤔 Do you know how long the delay is or is it varied on the time of year, as you say it’s not so much of a problem when it’s colder?

 

Hopefully someone from the community can also step in with any experience they may have if anything similar.

There is a fairly rapid drop in the temperature as soon as the DHW is completed - probably the result a pump over-run dissipating the heat, but in milder conditions and therefore cooler UFH flow temperatures of say 27-32C (with temp comp) the remaining few degrees of cooling can take and hour or two reach/match the UFH flow temp, then triggering the heat pump. 

Hey @Barry the bear,

 

I’ve tagged @juliamc, @James_N & @Speps to ask if this is something you’ve encountered before? I’ll also ask around to see if this is something the teams internally have heard of before and if they have any suggestions. 


Sorry I don’t know. I have a Daikin which is now monitored on heatpumpmonitor.org and you can see from this section of my graph from March when I was running the heating 24/7 (7deg outside temp) that my heating came back on within a few minutes after the dhw cycle.
You could look on their website for an Ecodan and check how that responds under similar circumstances to yours. There’s a link there to their forum where you will no doubt get some advice.

 

Thank you. The way your systems behaves is exactly what I’d expect. Mitsuibishi say they’ve at how mine operates and insist it’s working normally despite the long returning to heating the UFH.  Your suggestion I look at heatpumpmonitor.org is an interesting one, and I’ll certainly do that, unfortunately I don’t recall seeing my 4Kw HP (and packaged thermal store) listed there. The forum maybe useful.

 

Another forum you might try is renewableheatinghub.co.uk

Hey @Barry the bear, 

 

Thank you to @juliamc for stopping by and offering some insight and suggestions. Hopefully, this will help steer you onto the right path. Please keep us posted on how things progress. 🙂

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