Anyone got any thoughts on why my Vaillant Aerotherm Plus is performing a Legionella cycle with a 78C flow temp heating the water to 72C. I couldn’t find the official Vaillant docs but lots of interweb articles saying the standard Vaillant Legionella temp is 60C. At that temp if we jumped in the shower we’d get burnt so ideally I’d like it much closer 60, that said there’s no control in setting the Legionella temp. Any thoughts
It’s definitely 70+ °C they’re targeting, just not every heat pump can reach that. If you don’t have a backup heater, the legionella cycle stops whenever some internal temperature sensor triggers (it’s not the flow temperature - interestingly I can reach higher Legionella cycle temperatures in winter compared to summer as this trigger temperature is reached sooner in warm weather).
I don’t use the built-in legionella cycle but rather manually increase DHW temperature for a day when I want to do a legionella cycle. This is being automated in Home Assistant, and I have full control what the target temperature shall be.
Andre,
Doh, of course, I can set the legionella cycle by changing the target temp in HA via the MyVaillant integration. Great idea, I’ll do that and drop the temp to 60C
On a related note … I noticed in one of your previous posts that you use a circulator for the DHW. I live a 3 storey house and there’s a very old ‘beast’ of a circulator pump that is constantly on a dumb analogue timer from 7am til 10pm. I find my DHW efficiency drops through the floor when I have the DHW circulator on. I’ve experimented with different time windows but there’s not much improvement. My guy feel is the pump is circulating when it doesn’t need to be, but I have no data to prove that.
I was thinking of upgrading the pump to a more modern low wattage pump that can manage it’s pump time based on the temp of the water. Another option I was thinking was to put a pipe temp sensor on the upstairs bathroom and have HA control a Shelly Relay to switch the pump on
Curious how do you do your water recirculation and still keep it efficient. What cycle/timings work best for you and what pump do you use?
Many thanks in advance
Ian
Yeah, the circulation really eats into the DHW budget, especially if it’s on for a long time.
I have my pump on in the morning and evening for 90 minutes, coinciding with our usual morning/night routine. It’s also on during a Legionella cycle. I have temperature monitors on DHW outlet and circulation return on my tank and only stop the Legionella cycle once the return has reached 70°C.
As you don’t see any improvement on DHW use when the pump is off, I’m thinking you might have an issue with gravity circulation even when the pump is off. I had the same issue: the gravity brake valve was broken, so even when the pump was off a gravity driven circulation moved warm water up through the pipes and back down through the circulation return. You should definitely check whether you have such a valve and if you do whether it’s stuck/broken. The simplest test would be to turn the pump off, don’t use hit water for a couple of hours and then feel whether the DHW pipe leaving the cylinder is still warm. You might even feel it on the circulation pipe, but if circulation is slow it might have cooled down in the loop.
It’s definitely a good plan to make this smart. My pump is connected to a Shelly plug and managed through HA. It’s using around 5W max when active. Also having temp sensors on DHW outlet and circulation return give me the confidence that everything is always working as expected.
This is my pump. I would advise against getting this one - it has been working for two years but Aira installed two identical ones before that exploded (audible & smellable 
).
So you just have the temp sensors tucked in the lagging and you stop the circulation pump with HA when the temp on the DHW return reaches a certain temp?
For the legionella cycle I chose my setpoint to be 70°C and turn on circulation. This temperature cannot be reached in the center of my tank where the Vaillant sensor sits (stalls out at around 68°C). However I measure temperature in a top pocket, on the outlet of the cylinder and on the circulation inlet. As soon as the inlet temperature reaches my setpoint I know that all critical pipework has reached sufficient temperature. The rest of the time the circulation pump is purely time based.
This highly sophisticated piece of custom electronics is an ESP32 connected to the DS18B20 sensors reading the temperatures. It send the data via ESPhome to Home Assistant.
Thank @Andre_K as always. I’ll have a crack at putting the ESP32 together, I’ve been waiting for a project in order to learn ESP32 and ESPHome - this looks perfect
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It’s a great starter project. Let me know if you need any pointers!