Vaillant Arotherm plus compressor blocked during DHW run

Hardware Heatpump
1

Hi all,

I have installed a Vaillant arotherm plus VWL75 A/6 heatpump for my parents and they have used it for a little bit less than a year and it has worked fine so far. Since about 2 weeks the heatpump does not turn itself on anymore after a DHW run. After doing some investigations into the issue I noticed that when the flow temperature of the unit reaches about 55 degrees the unit turns off and the compressor is blocked for about ~63700 minutes.

When I reset the unit the heatpump turns on again as the blocking time is reset/cleared. Only to block the compressor again during the next DHW run when the flow temperature reaches about 55 degrees.

So far I have checked the circulation pump, the diverter valve, the magnetic filter and the control module (VWZ AI). The diverter valve operates normally as expected and can be operated trough the VWZ AI module. The circulation pump reaches about 1700 liters per hour when set to full power. The magnetic filter was also relatively clean, so there does not seem to be blockage of the hot water/heating circuit.

I also tried swapping the VWZ AI module with my own to see if the problem was in the VWZ AI module but that also did not change the issue. So therefore it seems to me that this either a configuration issue with the thermostat or a hardware issue with the heat pump itself

A factory reset also did also not offer any permanent relieve (this was actually the first thing I tried) it initially did make the issue dissapear for about 2 weeks but then it returned.

I am not really sure what to do next. Therefore I would greatly appreciate any suggestion, advice or ideas from you.

2

Hi Henry,

That is really interesting. I’m facing a really similar situation with an aroTHERM plus VWL 105/6.

The heat pump worked flawlessly for around 10 months and since July I had three « phases » of DHW failure.

To make it simple, situation is like yours : after running for couple of seconds or minutes if I’m lucky, the compressor got blocked due to minimal flow not reached. At that exact time, I can see on the inside unit that reported flow turned from 1800 to 0l/h. Which is incorrect because I can see flow with outside flow meter.

First time, I was able to recover from this after ± 12h and an hard reset on full system. I suspected configuration issue.

Next time, impossible to have it on even after hard reset. Because it failed for long time, i have been able to find out failure occured always when water was reaching 35c, so floor heating and cooling was working fine. After couple of days, it started to work again. I haven’t been able to identify any root cause to this.

For the third time, DHW failed for more than a week. At some point, yesterday, it worked again for no specific reason… 3 successful runs so far.

Whenever outside unit was blocked, inside unit did not pick up and got reported as « blocked » also.

At this stage, I’m waiting for Vaillant’s guy to come in but with this fantom issue I’m afraid he’ll be clueless.

My feeling, and because I tested couple of hardware items like you did, is that the issue is software related. Or I might be wrong and It could be either flow sensor (vortex) or main board failing…

What is the current status on your side ? I would be really interested to know if you made progresses and if a link can be found between your issue and the one I’m facing.

Could you tell me more on how you identified the « blocking period » you mentioned ? Also, do you have any ebusd instance running on the bus ?

3

Hey did you get anywhere on this? I’m having similar issue.

4

Hi

Yes, the flow sensor (vortex) has been replaced and it fixed the issue.

5

Hi all, I am still having this issue. Vaillant are meant to be coming, but I feel they might not be interested as they said the flow rate maxmium is too low (1750l/h) and wanted the installer to recify this - ive only had the unit three weeks. Does anyone have an idea on the below? For me it is NOT a flow issue, I have an idea of something else but I have three weeks experience. I am pretty anxious having spend a shed load of money and it’s going to be -7C on Friday.

Issue described below in chronological order:

Heat pump working fine

Heat pump does a domestic hot water DHW run

Either during of after DHW run it stops

Heating doesn’t restart

On Vaillant interface it gives errors – but no errors on app or sensocomfrot

Under live monitor

- Heating compressor blocked

- Anti cycle time 63773 min

Sometimes fault codes, sometimes not

Target flow is often low and equal to current flow temp (not as it should be on curve)

Fault codes

- F703 585 520 519 73

- F703 Sensor fault low pressure

- F585 Sensor fault Capc. Outlet Temp

- F520 Sensor Fault Building Circuit flow temp

- F519 Sensor Fault Building Circuit Return Temp

- F74 Building Circuit water pressure

Sometimes one ‘reset’ makes it work again, sometimes not. Sometimes needs lots of resets.

6

@Satwelsh I saw you comment elsewhere with helpful knowledge, do you have an idea?

7

I’ve found the exact same issue discussed on renewables heating hub:

8

Are you getting ~1750l/h with the pump power at 100%? If so, you have a flow rate problem, likely the primary pipework is too narrow/too long/too circuitous/all of the above.

Can you monitor a DHW run with your ebusd dongle and post the resulting graph with flow, return and DHW temps, as well as flow rate?

9

Yes 1750l/h.

Have you looked at the linked thread? It’s exactly the same issue and was electronic.

I unplugged the ebusd incase it was the cause, so it’s still unplugged, but issues persist. And the issue is now persistent and outside of DHW cycle also.

I don’t see how this is a flow issue (though our flow could be higher), because it worked for a few weeks, and still works sometimes. It’s completely irregular. Though I am pursuing the installer to come back and fix the flow issue - but it seems that’s not going to be easy.

10

Have you completely powered-down and power-cycled the entire system? Outdoor unit, all controls etc?

11

Yes for 10 minuts. I had to do it yesterday a few times, and today. Eventually after hitting reset on the machine a lot of time it worked again.

Vaillant Spain are coming thuraday to look.

12

Vaillent changed the circuit board in the machine today and it’s working again. Let’s hope it stays that way. And their independent action tallies with that fork the discussion above.

1 Like
13

Glad it’s sorted, hope you weren’t too cold in the mean time!

14

Good thing I kept the big log burner for emergencies!

Let’s hope its fixed for good. It’s now snowing outside and going to be down to -7C tonight and not much above 0 till Tuesday.

1 Like