Bob77 Posted October 20, 2022 Share Posted October 20, 2022 I recently had a Daikin Altherma split low temp heat pump installed. Since it was first commissioned at the beginning of the month and after two or three return visits from the installer it has consistently shown flow errors when producing DHW. Regardless of the target tank temperature, it will heat up to about 40-42C at which point the flow rate will drop from around 17 l/min to 4 or 5 l/min, and then to zero, at which point it will cut out with a 7H-01 error and then auto reset, then the same thing happens again. This then happens every 4 or 5 minutes until it finally gives up with a 7H-04 error. Once the tank cools down after hot water is used it will operate again but only until it reaches the same temperature. The radiator/underfloor circuit seems to work fine with the limited use it has had in this mild weather, but despite repeated system flushes and air purges, and the installer fitting additional air valves, nothing fixes the DHW issue. Can anyone give me any ideas what might be causing these symptoms, before the installer comes back? Indoor unit is EHVH08SU23EA6V. (What a catchy name!) Link to comment Share on other sites More sharing options...
dpmiller Posted October 21, 2022 Share Posted October 21, 2022 what is the deltaT across the tank coil when it first runs correctly, and then as the flow is reduced? Are there any other pumps in the circuit? Is this an inbuilt flow sensor, or an external flowsetter? Link to comment Share on other sites More sharing options...
Bob77 Posted October 21, 2022 Author Share Posted October 21, 2022 (edited) 43 minutes ago, dpmiller said: what is the deltaT across the tank coil when it first runs correctly, and then as the flow is reduced? Are there any other pumps in the circuit? Is this an inbuilt flow sensor, or an external flowsetter? I will make a note of the temperature numbers next time it runs. The readings give: Tank Temp, Leaving Water Temp, Inlet Backup Water Heater Temp, Inlet PHE Water Temp, Refrigerant Temp. Which of the inlet temperatures should I be looking at? The flow rate is from the built-in sensor. Pump wise there is a central heating pump in the airing cupboard next to the indoor unit and one on the UFH manifold downstairs. I am still learning about how it all works. I know it should be the installer’s problem to get it working but I’d like to understand the cause in case of future problems. I have the DHW set to come on overnight (we are on Economy 7). I had turned the tank target temperature up to 55C (higher than I will want it but I wanted to see if it could get there). This morning it had reached 47C, with the usual errors. When I check the malfunction log it had 13 water flow errors, basically every 4 minutes between 1am and 2am. This implies it has been cycling on and off repeatedly to try and get that last few degrees, which I am worried will be damaging the compressor. It has also been completely unable to get hot enough for the legionnaires cycle, so it shows that warning continually. Edited October 21, 2022 by Bob77 Link to comment Share on other sites More sharing options...
Bob77 Posted October 21, 2022 Author Share Posted October 21, 2022 Ok, just turned it on. Tank temperature is currently 32C with a target of 55C. current readings when just switched on: Tank temp 32C Leaving water temp 25C inlet backup heater water temp 25C inlet PHE water temp 25C Refrigerant temp 25C Flow rate 0.0 l/min. after a short while once the refrigerant temp reached 42C the pump switched on and the flow rate is now 16.8-17.4 l/min. Refrigerant temp dropped to 28C as leaving water temp started to increase. Now 5 mins after switching on: Tank temp 32C Leaving water temp 33C inlet backup heater water temp 33C inlet PHE water temp 29C Refrigerant temp 29C Flow rate 16.8 l/min. Link to comment Share on other sites More sharing options...
Bob77 Posted October 21, 2022 Author Share Posted October 21, 2022 It ran for about 40 mins before quitting with the flow error. last readings I noted, about 2 or 3 mins before it stopped were: Tank temp 44C Leaving water temp 52C inlet backup heater water temp 53C inlet PHE water temp 47C Refrigerant temp 51C Flow rate 16.8 l/min. I didn’t check it after this point but from past experience the flow will have gradually slowed down over the course of a minute or so before reaching zero at which point the pump cuts out. When it stopped the tank had reached 46C. I’ve switched it off again now to avoid repeated cycling. Link to comment Share on other sites More sharing options...
Bob77 Posted October 21, 2022 Author Share Posted October 21, 2022 I just ran it again after we had used some hot water and this time watched what was happening with the readings. The difference between LWT and inlet PHE temp (I assume this is the delta T you mean @dpmiller?) was fairly steady at 5C to 6C. At the point where the flow started to reduce the LWT was 50C, inlet temperature 45C and tank temperature 44C. As soon as the tank reached 44C I could hear the pump slow down, the flow rate dropped from the usual 17.4 l/min to zero within about 30 seconds. Another 30 seconds after that it switched off with the water flow problem error. For whatever reason as soon as the tank temperature gets up to that level the flow drops right down. Link to comment Share on other sites More sharing options...
dpmiller Posted October 22, 2022 Share Posted October 22, 2022 Any chance it's plumbed incorrectly? 45C could very well be the DHW blending valve's setpoint... Photos of the install would help, here. Link to comment Share on other sites More sharing options...
ProDave Posted October 22, 2022 Share Posted October 22, 2022 Is there a motorised valve operating from a tank thermostat and the tank thermostat is set lower than the ASHP target tank temperature? Picture of the plumbing and controls on and around the tank? There should be a motorised valve and tank thermostat on an UVC as a safety measure to shut off the heat input if it gets too hot. This is often not actually used with an ASHP and in my case the tank stat is set to 65. Link to comment Share on other sites More sharing options...
Bob77 Posted October 22, 2022 Author Share Posted October 22, 2022 The tank is integrated into the indoor unit so there’s not much to see without taking it all apart, which I don’t want to do at this stage because if there is a problem then I don’t want to be liable for messing around with it! The pump at the left is connected to the wireless thermostat receiver from the bedroom thermostat (radiators) Link to comment Share on other sites More sharing options...
Bob77 Posted October 22, 2022 Author Share Posted October 22, 2022 (edited) Plumbing into the top of the indoor unit. Probably not much help as all the interesting stuff will be inside, I imagine? (Lagging has been removed as an additional air valve was cut into the pipework) Edited October 22, 2022 by Bob77 Link to comment Share on other sites More sharing options...
dpmiller Posted October 22, 2022 Share Posted October 22, 2022 what's the item above and to the left of the pump? /if this is a split with inbuilt tank, and only heating flow and return coming from it, it would seem to me to be an internal fault as there is no external flow for DHW... Link to comment Share on other sites More sharing options...
Bob77 Posted October 22, 2022 Author Share Posted October 22, 2022 2 hours ago, dpmiller said: what's the item above and to the left of the pump? /if this is a split with inbuilt tank, and only heating flow and return coming from it, it would seem to me to be an internal fault as there is no external flow for DHW... The black cylinder? That’s the low loss header I believe. I’m also starting to suspect some kind of internal fault. The space heating circuit seems to work fine but the hot water has never worked properly since installation. It won’t even get up to temperature when it tries to run a legionnaires cycle. Link to comment Share on other sites More sharing options...
Bob77 Posted November 14, 2022 Author Share Posted November 14, 2022 A very belated update on this. The installer has been back, flushed the system, run air purge and test cycles and can't find the cause so it looks like there's either a faulty valve or sensor somewhere. The flow errors also crop up in space heating mode but only about every 15 minutes rather than every 4 minutes in hot water mode! A Daikin engineer was meant to visit last week, after two weeks of chasing by the installer, but never showed up. I have another appointment tomorrow so hopefully I will actually have properly functioning heating before the weather turns cold. Not too impressed with this system, or Daikin's customer service, so far! Link to comment Share on other sites More sharing options...
LT2023 Posted October 16, 2023 Share Posted October 16, 2023 Hi, so what was the end of this story? I have the same problem with my Daikin Altherma 2 long time. I have change the boiler, bigger diameter pipes (25 mm plastic Uponor system) from Daikin to boiler (200 litres). Have I bypass valve, but I don't know if that valve is a must, because I have seen Dainkin 2 like ny without bypass valve. Link to comment Share on other sites More sharing options...
Bob77 Posted November 1, 2023 Author Share Posted November 1, 2023 Hi @LT2023, I just saw this message. I meant to post an update last year but evidently forgot! A Daikin engineer showed up and replaced the flow sensor and it was worked without a hitch since then. I've only had the heating coming back on for the last couple of weeks and might need to adjust the WC curve to get optimum performance but I have not had any errors. I suspect the sensor might have been damaged during installation. Link to comment Share on other sites More sharing options...
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