JohnMo Posted November 14, 2023 Share Posted November 14, 2023 9 hours ago, JamesPa said: For example the Vaillant R290 Heat pumps don't rely at all on a tank immersion, and SOFAIK aren't even capable of controlling one. The manual for the interface controller, uses the terminology backup heater and immersion throughout. This is used for a legionella function, DHW and heating. It can control cylinder immersion and external heater module. There is also a – Limp home mode Immersion heater: Heating/DHW They (Vaillant) sell a 6kW backup heater module and the heat pump interface controller, controls it. An R290 heat pump may not need external electric elements in the heating or DHW, but they certainly provide for it in abundance. Way more control of external heating than my R32 unit. Link to comment Share on other sites More sharing options...
JamesPa Posted November 15, 2023 Share Posted November 15, 2023 (edited) 12 hours ago, JohnMo said: The manual for the interface controller, uses the terminology backup heater and immersion throughout. This is used for a legionella function, DHW and heating. It can control cylinder immersion and external heater module. There is also a – Limp home mode Immersion heater: Heating/DHW They (Vaillant) sell a 6kW backup heater module and the heat pump interface controller, controls it. An R290 heat pump may not need external electric elements in the heating or DHW, but they certainly provide for it in abundance. Way more control of external heating than my R32 unit. Strange. I was aware of the Vaillant backup heater (is it just a very expensive Willis heater in a box I wonder) but in nearly 80 pages of system diagrams https://www.vaillant.co.uk/downloads/aproducts/renewables-1/arotherm-plus/arotherm-plus-1/quick-guides/all-schematics-wiring-notes-1799366-2626556.pdf not one (so far as I can see) shows any electrical connection between the heat pump interface board and immersion heater. So its presumably a function of the interface unit/controller which they don't consider an essential part of the system? My (putative) installer has confirmed that the Vaillant 290 does the legionella cycle natively (ie without the immersion - which given that it can get to a FT of 75 is entirely believable and the heat pump manual appears to confirm) but of course that doesn't mean that it might not be capable of controlling an immersion. Prior to R290 the use of the immersion heater for legionella control would presumably have been necessary, and they probably haven't changed the interface board/controller. 12 hours ago, JohnMo said: There is also a – Limp home mode Immersion heater: Heating/DHW I cant see how a 'limp home' mode based on an in-tank immersion works for both CH and DHW if there is a diverter valve, unless the diverter valve itself has a 'limp home' setting or a bypass! My thought was to omit/ignore the immersion heater from the tank, and then a 'backup heater' inline with the heat pump can serve as a limp home both for DHW and CH, as well as a booster for exceptionally cold weather (of course the first of these depends on whether the water pump continues to work in heat pump failure mode). Currently this is more of a 'thought experiment' than an actual plan, because its convenient to have a wholly separate immersion to feed excess solar into (subject to the usual discussion about what the optimum strategy is for summertime excess solar/heat pump/immersion). However doing this would become very attractive if, by omitting the in-tank immersion heater altogether, and putting suitable protective measures around the Willis heater/heat pump combo, the need for a vent to the UVC is avoided. There is also something rather satisfying about having one component perform several functions, and having all of the heating elements of the system in one place feeding one set of plumbing. Edited November 15, 2023 by JamesPa Link to comment Share on other sites More sharing options...
DCD83 Posted January 24 Share Posted January 24 Hi, how can I tell if the pump is working on the heating or the hot water? I was told that the hot water will stay hot in the tank and when I use it, cold water will flow in and when it drops to a certain temp (don’t know what temp) it’ll kick in and heat the water up. If I have the 3 lines on, my system seems to be heating the water 24/7 and it’s costing a fortune. If I turn off the 3 lines then the water will drop endlessly and was 8 degrees yesterday. I want it to run when it only heats up once it drops to a certain temp but I can’t figure out how to set that as it’s either heating 24/7 or not heating at all. Any help please? TIA. Link to comment Share on other sites More sharing options...
ReedRichards Posted January 25 Share Posted January 25 (edited) 15 hours ago, DCD83 said: my system seems to be heating the water 24/7 and it’s costing a fortune That's not possible. The water will be heated to whatever temperature is set and then that heating will stop. If that fails there is a safety cut-out that will stop the hot water tank getting dangerously hot. It would only cost a fortune if you have left a hot tap running so the hot water flows away as fast as you can heat it. Also, hot water heating is normally given priority over space heating so you would have no heat in the house if your hot water was being heated all the time! So your system may be set to heat the hot water as necessary 24/7 but it will only actually heat the hot water when the tank temperature drops a certain number of degrees below the set temperature. You might be able to change this number but I don't know Midea units so i can't tell you how. For what its worth, in the hour before I get up I heat my hot water cylinder to 55 C with cheap rate electricity. Then during the day the set temperature is dropped to 44 C just to make sure the water in the cylinder doesn't get too cold if we use a lot of it. And at night it's off completely so the heat pump does not come on unexpectedly and scare the owls. Edited January 25 by ReedRichards Link to comment Share on other sites More sharing options...
PhilT Posted January 25 Share Posted January 25 16 hours ago, DCD83 said: Hi, how can I tell if the pump is working on the heating or the hot water? I want it to run when it only heats up once it drops to a certain temp but I can’t figure out how to set that as it’s either heating 24/7 or not heating at all. Any help please? TIA. Your photo shows that your heat pump is currently heating your radiators (heat pump symbol bottom left). Hot water is "on" but in standby mode. There are several YouTube videos showing how to use this controller. There is one about the hot water timer - you could use that instead of leaving it on 24/7, that's what I believe most people do. Link to comment Share on other sites More sharing options...
JohnMo Posted January 25 Share Posted January 25 Are you sure you don't have a mid point valve/actuator instead of a diverter? Link to comment Share on other sites More sharing options...
DCD83 Posted January 25 Share Posted January 25 Okay, but why does my hot water either stay at the temp I set it to ie 46 degrees if I leave the hot water on, and then if I turn it off then it just continues to drop endlessly to 0. To get the hot water to kick in and heat back up if it drops a bit, do I need to leave the hot water on or turn it off? Sorry if that’s not clear but basically my water either stays at the set temp all the time or the only other setting I’ve found is to turn the water off but then it never heats up and will drop to 0. What I want is a middle ground where it heats up to say 46 and then drops as the tank gets cooler over several hours and then when it gets to say 26 I want it to kick in a heat back up to 46. I can’t figure out how to set this or whether I need to leave the DHW powered on in the app or switch it off in the app? Either way that never happens. Link to comment Share on other sites More sharing options...
sharpener Posted January 25 Share Posted January 25 Perhaps as a result of some misconnection the tank is losing heat to the central heating circuit(s)? Maybe that's what @JohnMo was implying. Link to comment Share on other sites More sharing options...
Beelbeebub Posted January 26 Share Posted January 26 As pointed out before, if there is a fault with the diverter valve setup so that there is flow through the tank coil during heating mode, the hotter water in the tank will be cooled by the water passing through that coil at the cooler heating flow temp. Symptoms would be Your tank swiftly loses temp only when the heating flow is on. The return flow out of the tank coil (usually the lower pipe) is warmer than the feed flow in (usually the upper pipe) If your controller is set to hot water priority it will start heating the house, then notice the tank has cooled, switch to heating the tank, then go back to heating the house, then notice the tank had cooled.... And so on. Try setting your hot water to timed. At this point the above won't happen outside of the hot water times but you would quickly see the tank temp drop to the heating flow temp and then stay there. If there is not a diverter fault then another possibility is the tank is losing temp naturally. Because the prove is at the bottom it can only "see" the temp there. As the tank loses temp naturally the cooler water sinks to the bottom. Your probe will "see" cool water but be unable to know the water above is still hot. My tank can be half full of 65C water and the bottom be at 20C (I have multiple sensors). Again, if your hot water us set 24/7 it wouldn't take much demand or cooling to trigger another heating cycle even though there is ample hot water left Link to comment Share on other sites More sharing options...
HughF Posted January 27 Share Posted January 27 The midea will say ‘on dhw’ in the middle when it is doing hot water reheat. I can’t find what the setpoint is for a dhw reheat in any of GH’s videos, but suspect it to be 10-12 degrees. When it’s heating radiators it will just say ‘on’ in the middle…. Link to comment Share on other sites More sharing options...
HughF Posted January 27 Share Posted January 27 Midea installer manual attached…. Nowhere in there can I find what the dhw hysteresis is set to by default. 1063-Midea-Installation-Manual-2021-for-web-FHP.pdf Link to comment Share on other sites More sharing options...
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