Can anyone help me please? I’ve got an Arotherm Plus Heat Pump and there doesn’t seem to be any heating or hot water in the house. I have to put my immersion on instead of the heating to get hot water. On the Live Monitor panel it says 3 things: DWH Pre Run, Flow Rate Too Low, Compressor Blocked. I’ve bled the radiators and there’s water on all of them and I had a plumber come in and investigate. They released an airlock to the unit but still no central heating. I have 3 zones, 3 circuits all set to heating, but still the control panel is showing 0.0kwh though the bar and pressure is all correct
@JohnT1 sounds like there’s a block somewhere!? Can you get the installer out to check it? Has the heat pump been running ok up to this point? anything changed that you can think of if so?
Yeah I had the installer come out yesterday, there was an airlock, they checked all the valves, pumps and had an electrician over as well and they were all okay. The pump was installed a month ago and never turned on the heating since it was hot so it looks like we’ve had no heating or hot water the whole time so we’ve had to use immersion heating for hot water
Why did they leave yesterday without sorting it? Surely it’s their problem to fix?
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They tried again today but no luck might be best if I get a vaillant service man to come
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I wonder if there’s an issue with the central heating pump in the outside unit? or a valve in there that’s closed… @Andre_K any ideas?
Did they check the strainer?
DHW Pre Run indicates the pump being turned on shortly before the compressor turns on - I see this every day on my DHW runs so that’s a normal state. Compressor Blocked is also a state I see in normal operation. The flow rate error definitely sounds like the culprit. Can you see on your live monitor what the flow rate is when the system tries to run? Definitely sounds like an issue with the outdoor pump or the flow rate sensing.
I fit Vaillant heat pumps as my go too, the issue is air stuck in the pump that’s why it comes up with compressor blocked. You can either isolate flow or return at the pump and slacken one of the unions so it pulls it through the pump getting rid of the air or go to test programs and put the heating on test and that sometimes unblocks it.
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Yeah it looks like the building circuit flow is at 320 l/h which is low for a 7kw unit I think, do you think it may be the magnetic filter or the brass strainer?
Trying to do it with the test program with the heating, how long should I leave the test run for? Don’t really know anything about heat pumps or plumbing so not sure how to isolate the flow and such
Is that for DHW or heating? On the indoor unit you can set up pump speeds for DHW and heating. I have them on auto. Also there’s a setting for max. rem. head, which indicates how much pressure drop the pump expects from your heating system. Put it to 900 (max) to get maximum flow.
Edit: Sorry - I have no experience with the magnetic filter or brass strainer. I’m just an end user and never had to deal with these 
Both DHW and heating, got no heating at all and from the radiators and no hot water, have to put the immersion on for hot water at the moment, I’ll see if there’s a max flow setting on the control panel in the installer level
I meant the 320 l/h flow rate - when do you observe this?
I can video call you if it helps on Sunday to try and get it going
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I had that problem just after I completed my own installation. Since I installed a Fill & Flush valve, I tried running mains water through one side, around the whole system, and out the other - but no joy. So I swapped then around (reversed the flow) and boom !!!
Related question for Tristram please.
With a 7kw Vaillant is it better to run at max flow rate? Mine’s around 19l/m with dt across flow and return of about 2.0-2.5 deg.
Or is it better to lower the flow rate (max remaining head) to say 11 l/m and get a higher dt (ideal 5deg?).
Reason I ask is earlier in the year about 6months after install I had flow rate of around 12 l/m due to crud in strainer and mag filter. However I did notice the dt was higher due I guess to lower flow rate.
Obviously I did the right thing by removing crud but am I getting more flow than is efficient?
FYI I have an ‘open’ system with no hydraulic separation and all rads fully open. Very happy with it but can I optimise by lowering flow rate?
If your house was still as warm as you wanted with the lower flow rate, you can safely lower it now with the remaining head option and would save some (very little probably) money on the lower electricity cost for the pump.
Alternatively, maybe you could lower your flow temperature a bit and keep the flow rate at max, which might improve COP a bit and save you a bit more electricity than lowering the pump speed.
If you don’t want to tinker with that, just lowering the pump speed would work and is easily reversible in cas it doesn’t get warm.
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