Posted by: @anon67

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I have a 3 year old 10kW vaillant aroTherm heat pump connected to dhw and ufh.

The heat pump kicks in on demand for hot water but when it comes to heating it faults, getting a mixture of faults 

F.732 Compressor outlet temperature too high

F. 733 Evaporation temperature too low

F. 0521 Outdoor temperature sensor signal invalid

Does anyone have any ideas how I can get the heating back on even temporary? Until I can get someone to look at it on Monday. 

I tried looking through the menu but there doesn't seem to be any option to force heat. 

When I had a series of apparently unrelated faults my installer turned up, checked the flow rate using the test menu, and cleaned the filters (two - a mag filter and a gauze filter immediately behind the unit).  Fixed the problem.,  He told me that 90% of call outs are that.  None of the apparently unrelated faults said anything about flow rate!

That said the fact it heats hot water suggests its not filters so...

If you go into live monitor on the HPAI and look at the first screen it initially shows --.  Until my installer showed what to do at this point I have always 'clicked past'.  But if you wait a few seconds on that screen it gives you a stream of consciousness about what the heat pump is doing.  That may reveal something.

@jamespa

On the live monitor I'm getting 

"Heating compressor blocked"

"Evaporation temperature too low"

Also had a new fault code this morning, 

F. 823 Hot gas temperature switch open

I found a fault code list which gives a cause/remedy

F.732 Compressor outlet temperature too high - Application limits exceeded - Check compressor inlet/outlet sensors; Inspect refrigerant volume

F.733 Evaporation temperature too low - Insufficient air volume flow through the outdoor unit's heat exchanger - Check fan unit for dirt; Inspect EEV operation; Check refrigerant volume

F.823 Hot gas temperature switch open - Hot gas thermostat shut down the heat pump due to high temperature - Check EEV; Replace dirt filter in the refrigerant circuit

@anon67 

Sorry I cant help. 

The only 'lead' you might follow is the fact it works for DHW.  The faults look like they would affect DHW also but apparently they don't which could indicate that they are artefacts of some underlying problem, perhaps one that the heat punp cant itself diagnose.  Have you got a failed pump or a blockage downstream in the UFH that does not affect the DHW, or even just a blocked diverter valve?

@jamespa

Going off those faults it's looking more towards a blockage of some sort. 

I had a look at the diverter valve, it's a honeywell v4044c, I can move the valve to the open manual position and when I test the valve through the installer menu of the interface you can here it pulling across back to auto when testing heating. Unsure if it's actually moving internally though.

@anon67 when was it last serviced? 1st thing to do is switch it off, clean the outdoor coil thoroughly with a watering can of gently warm water maybe 4 cans to drag the non visible dirt form the fins, then isolate and check / clean the inline filter and then check from there. (this is not a service but will likely help)

Also do you have a bypass on the flow, low loss header or an open loop system to allow the minimum flow passed any emitters with closing valves? 

What you are describing is a lack of heat exchange on both the high and low side of the refrigerant circuits, the good news for you is if you can rule out the flow, filters, and air flow across the coil Vaillant will come out under warranty as long as you have had it serviced in the last 12 months.

The fact that it only happens on heating could be:

A- its relative to a loading issue so the DHW only needs around 4kW the home may need 10kW and the issues are heat exchange on full load.

B- there is a circulation issue with the heat exchange when in heating mode due to lack of open circuits, air in emitters or lack of bypass

C- there is an issue with your diverter on the change from DHW to heating (we AAC only use priority DHW diverter and not 2 ports but there are many 2 ports) if you have them it may be one is closing and the other not opening.

@ashp-bobba

It has been recently serviced, October 25.

I did call vaillant & installer but shut until Monday

I didn't try with water but it was iced up (assumed that was the fault as that had happened once before a week or so after being installed worked after it thawed) so I got the hairdryer out and defrosted it completely before trying to switch it on again, I can look through the front and see daylight through the fins.

I'm not sure on the bypass, I will have a look and take a picture once I get home. 

It has been recently serviced, October 25.

I did call vaillant & installer but shut until Monday.

A - That's interesting, I didn't know that. Potentially why it's starting on dhw demand from initial startup then faults when switching.

B - Unsure about the bypass however every single zone on both ufh manifolds are open. I upped all the grundfos to the second speed to try and see if an increase in the flow would assist to no avail.

C - After a quick Google I believe the honeywell v4044c is a dhw priority, haven't tried to open it up yet.

@anon67 Well its just a few things you can check that rule out some very common issues, I hope it helps you get passed the issue.

Even if you can see daylight through the coil it can still be covered by a very fine layer of dirt which does effect it a little, if you had it serviced in October I am sure it is fine.

We see several new customers come to us with the same issue that in DHW it works find a trips once changed over to heating, nearly always its blocked filters and coils, it could also be something else though, if it is refrigerant then the manufacturer will likely repair for free as Vaillant tend to have good warranty on the actual HP.

@ashp-bobba

Yeah I'll give it a go, will check filters as well. 

Thanks for your suggestions. I'm hoping it's something repairable, no heating in the house with kids at this time of year is not ideal. 

No ideal if it's possible or not but I need to look into a back up. Maybe something like an immersion heater and a way to allow circulation pump to feed the ufh in case this happened again.. That's thought for another day though!

Posted by: @jamespa

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When I had a series of apparently unrelated faults my installer turned up, checked the flow rate using the test menu, and cleaned the filters (two - a mag filter and a gauze filter immediately behind the unit).  Fixed the problem.,  He told me that 90% of call outs are that.  None of the apparently unrelated faults said anything about flow rate!

I love it, and quite honestly this such great advice @jamespa… if you have an obscure error or fault code on your heat pumps control panel, irrespective of what the manual says it might or might not be, turn the pump off and go and clean your filters or Y strainer. 

Posted by: @ashp-bobba

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Even if you can see daylight through the coil it can still be covered by a very fine layer of dirt which does effect it a little, if you had it serviced in October I am sure it is fine.

I wouldn’t be so sure, @ashp-bobba. In my experience, the number of services that don’t include coil cleaning is probably the majority. Too often it’s little more than a visual inspection, a few beep-beep-beeps on the controller, and, if you’re lucky, a strainer or filter cleaned.

My personal favourite was a recent post from @outlawuk, where he pointed out that Global Energy Services’ service specification explicitly included cleaning the evaporator tray… yet a dead mouse was still sitting there after the service. 

@editor hmmm, our engineers Rae, Craig, Naz, Rob and Ryan literally take the fan out and washes the coil back though the opposite way the air flows, I am ever the optimist assuming maintenance is done well. 

If we were to investigate this systems we would check the following items in this order and test at each stage before breaking a refrigerant circuit, the items with a * should be ok for some home owners to check.

*Main circuit strainer 

*Main filter if fitted

*3 port diverter / 2 port are open correctly in heating mode (as the issue is in heating)

*water pressure 1.7-2.4 barr (design relative to static height and pressure)

*air bleed from system circuits 

*all isolation valves are open in correct position by moving them closed and open again 

*wash through evaporator coil 

*check flow rate is at 28-29lpm 

*check all TRV's actuator heads and stats are on and open 

*check flow rate temp from Vaillant control  

*read all sensors on controller and note down while running and settled

If the above does not reveal the issue and sensors are reading something not good like 120C on compressor or -3 on super heat then we would break the circuit with gauges and run / test / recover / repair leak and recharge (or call Vaillant to do this part for free if running low)

Note: I would also test all of this in DHW mode because if in DHW mode the system runs fine it is not refrigerant but very likely heating circuit related.