Arotherm (not +) wiring handbook

[HughF]

I’ll be fitting a used 5kW Arotherm soon, does anyone have a copy of the wiring diagram/instructions easily to hand? I’ve downloaded the installation manual but they don’t appear to be in there.

 

Simple install; single zone, open loop, dhw cylinder, Vaillant controls.

[sharpener]

Try this FB group. The wiring diagrams are part of the Vaillant schematics files (in Files section). I doubt they have changed much, the VWZ Appliance Interface looks quite antiquated and I think pre-dates the plus range. Or post a query there.

Which controls are you planning?

Edited Thursday at 12:21 by sharpener

[JamesPa]

As @sharpener says they are in the schematics.

 

Not much to be done TBH, everything converges on HPAI. 

• 2 wire bus connecting heat pump , HPAI, WiFi transmitter and wireless interface to sensocomfort/outdoor sensor
• Connection to sensor in tank
• Connection to Diverter valve

Thats it (other than power of course.)

 

[sharpener]

I would go with the wired SensoComfort if you can, as the wireless ones also come with a wireless OAT sensor and there are frequent reports of problems/error messages/solar cells needing cleaning.

[HughF]

Thanks for the info all….

[sharpener]

One last thing. Vaillant have recently changed the spec for the fancy RCD you will need, previously the cheap(ish) one from Fusebox was approved but now IIRC the only one is from Haager. This topic is a whole nightmare in itself.

[-rick-]

Not Valliants fault the electrical standards were clarified that these things were required.

[sharpener]

It's well established that Type B RCDs are required with HPs that have inverter drives. What is new is that Vaillant have themselves added new requirements regarding (I think) harmonic content that means that only certain Type B RCDs are suitable - which makes a mockery of the type classification system.

 

Personally I think this stuff is massively overdone, safety is mainly a matter of workmanship not added devices. The house my parents bought in 1953 was rewired to (the then) ring main standards with Wylex ceramic rewirable fuse carriers but I don't remember them blowing as a regular thing. RCDs and MCBs were a significant improvement but I am not convinced that ordinary domestic installations truly need surge protection or arc fault detection. /rant.

IMO  the HP mfrs should build whatever protection is required into the HP itself, then (a) you could connect them into an ordinary CU final circuit (b) there would be no debate or confusion in the trade (c) ppl could not undercut reputable electricians trying to do a proper job by fitting a cheaper RCD or ignoring the requirement not to fit it downstream of one with lesser protection.

[SimonD]

9 minutes ago, sharpener said:

It's well established that Type B RCDs are required with HPs that have inverter drives. What is new is that Vaillant have themselves added new requirements regarding (I think) harmonic content that means that only certain Type B RCDs are suitable - which makes a mockery of the type classification system.

 

Some are now asking for type F RCDs only. And some want mcb and rcd type b for protection.

[-rick-]

11 minutes ago, sharpener said:

IMO  the HP mfrs should build whatever protection is required into the HP itself, then (a) you could connect them into an ordinary CU final circuit (b) there would be no debate or confusion in the trade (c) ppl could not undercut reputable electricians trying to do a proper job by fitting a cheaper RCD or ignoring the requirement not to fit it downstream of one with lesser protection.

 

I think the RCD is to protect the cable so inside the heatpump doesn't necessarily work. You do make an argument that the manufacturers should install better filtering inside the unit so the noisy signals that need complex RCDs don't leave the unit. That would impact efficiency though I'd guess.

[JamesPa]

49 minutes ago, -rick- said:

I think the RCD is to protect the cable so inside the heatpump doesn't necessarily work. You do make an argument that the manufacturers should install better filtering inside the unit so the noisy signals that need complex RCDs don't leave the unit. That would impact efficiency though I'd guess.

The point @sharpeneris making, quite correctly imho, is that heat pumps and other equipment should protect themselves from anything that the manufacturer deems it's necessary for the equipment to be protected against.  Then local electrical regulations should mandate what is deemed necessary to protect the cable and people. 

 

That's a logical split.  Anything else is equipment manufacturers stepping into the scope of building electrical regulations, which they have absolutely no business doing.

 

Btw RCDs principally protect people (they trip before a person receives enough of a jolt to be killed, at least mostly) mcbs protect cables (they trip before the cable sets fire due to overload).

Edited 18 hours ago by JamesPa

[JamesPa]

2 hours ago, -rick- said:

Not Valliants fault the electrical standards were clarified that these things were required.

Can you provide a reference please.  Most recent I can find says that RCD protection (or not) for fixed external plant is down to a risk assessment to be carried out by the electrician.  

Edited 18 hours ago by JamesPa

[-rick-]

8 minutes ago, JamesPa said:

The point @sharpeneris making, quite correctly imho, is that heat pumps and other equipment should protect themselves from anything that the manufacturer seems it's necessary for the equipment to be protected against.  Then local electrical regulations should mandate what is deemed necessary to protect the cable and people.  That's a logical split.  Anything else is equipment manufacturers stepping into the scope of building electrical regulations, which they have no business doing.

 

If the regs say something along the lines of appropriate RCD protection needs to be installed. Then you need to choose the appropriate RCD. RCDs come in many flavours and the issue here is that Valliant heatpumps put out waveforms of a higher frequency than standard RCDs can protect against. If they installed filtering in that heatpump to eliminate the higher frequencies then such RCDs would not be required.

 

That the manufacturer recommends something is a consequence of them helping installers meet the regs for their device as currently designed.

[-rick-]

6 minutes ago, JamesPa said:

Can you provide a reference please.  Most recent I can find says that RCD protection (or not) for fixed external plant is down to a risk assessment to be carried out by the electrician.  

 

After posting that I checked, it might not be regs that I saw updated but installation guidance:

 

https://www.heatpumps.org.uk/wp-content/uploads/2025/03/HPA-RCD-Guidance-March-2025-Final.pdf

 

Edit: quoting from that: BS 7671 Regulations 134.1.1 and 510.3 both require the installer to take account of the manufacturers’ instructions

Edited 17 hours ago by -rick-

[JamesPa]

1 hour ago, -rick- said:

 

After posting that I checked, it might not be regs that I saw updated but installation guidance:

 

https://www.heatpumps.org.uk/wp-content/uploads/2025/03/HPA-RCD-Guidance-March-2025-Final.pdf

 

Edit: quoting from that: BS 7671 Regulations 134.1.1 and 510.3 both require the installer to take account of the manufacturers’ instructions

Interesting.  I guess this is the heat pumps association trying to do the electricians assessment for them, so potentially consistent with the guidance from the IET that I read.

 

Included in the March 2025 document is this:

 

Quote

 

4. Do the Wiring Regulations (BS 7671) have explicit requirements for heat pumps?

 

S 7671 (IET Wiring Regulations) does not contain any specific requirements for the installation of RCDs for additional protection on a circuit for a heat pump. The additional requirements are intended for socket-outlets and mobile equipment for use outdoors, and under these circumstances do not apply. Selection of an RCD for a heat pump circuit therefore follows that for other electrical equipment and is covered in the current regulations. The most likely requirement to install an RCD will be because of the type and/or T h e H e at Pu m p As s o c iat io n w w w. h e at pu m ps . o r g. u k 6 installation method of the cable supplying the heat pump (regulation group 522.6) and device selection is covered in Regulation 531.3.

 

5. When would a circuit for a heat pump not need RCD selection?

 

Additional RCD protection is not required where a cable is installed in accordance with one of the methods described in Regulation 522.6.204 indents (i), (ii), (iii) or (iv), where cables in the circuit have mechanical protection to prevent penetration by screws, nails, drilling etc (such as earthed metal armour, metallic conduit or metallic trunking). While this is not typical for existing supplies, it could allow supply design to negate the need for an RCD. However, manufacturer’s instructions must be taken into account. Any impact of this approach on product warranty should be understood

 

 

So it clearly says that there are times, according to the March 2025 document, when no RCD protection is required.  

 

So far as I can tell (I dont have direct access to the source material) Regulation 522.6.204 concerns concealed cables installed less than 50mm deep outside the prescribed safe zones (the safe zones are essentially horizontally or vertically from any switch or outlet or within 150mm of a  corner of any room including the corners where walls meet floor or ceiling.  Cables installed outside the safe zone need mechanical protection against nails, screws etc.

 

I suspect that most cables are, in practice, either surface mounted (ie not concealed) or installed in safe zones, or (under floorboards) more than 50mm deep.  Certainly that is true in my house.

 

So if this applies to the ASHP circuit, and unless there is a warranty impact or the manufacturers instructions state otherwise, no RCD is required, according to the March 2025 document.  

 

Coming back to Vaillant @sharpener, (and @-rick- the issue of manufacturers instructions) the version of the Vaillant installation manual I have from 12 months ago does not specify that RCD protection is required, what it does specify is that if an RCD is required then it must be of a particular type.  This seems still to be the case according to the installation manual here but this manual also seems still to specify type B without any specific additional requirements. 

 

I do have an interest in this.  My trusted electrician fitted the circuit up to the isolator switch with just MCB protection and was adamant (12 months ago) that this was correct.  I was and am happy with this decision.  Since the cable is visible throughout its length, that is entirely consistent with the document referenced above.  The heat pump engineer then connected my Vaillant heat pump up to the isolator switch using a length of armoured cable which is partially hidden (under a kitchen unit) but anyway entirely within the safe zone.  From the document above armoured cable wasn't actually necessary, but I'm not complaining!  Since at the time (and maybe now) Vaillant did not specify that RCD protection is required, the whole installation appears to be correct at least at the time, and maybe now if Vaillant are still only specifying the type of RCD if one is required.  Phew.

 

Of course (in most if not all cases) there is nothing wrong with fitting an RCD even if it is not required.  It will provide additional protection.

 

Edited 16 hours ago by JamesPa

[-rick-]

5 minutes ago, JamesPa said:

So it clearly says that there are times, according to the March 2025 document, when no RCD protection is required.  

 

That is my understanding. If the cable is otherwise protected its fine, but at least on retrofit installs doing so may be tricky.

 

5 minutes ago, JamesPa said:

Of course (in most if not all cases) there is nothing wrong with fitting an RCD even if it is not required.  It will provide additional protection.

 

Only if to the right spec, hence need to follow the manufacturer.

 

As an aside, either I'm missing something or it feels like the regs are calling out heatpumps, etc, but ignoring a whole load of other devices that could be as problematic or more. I suppose BIG heatpumps could be more of a risk but smaller heatpumps aren't drawing much different power from many other home devices these days that will also have issues with high frequency leakage. Induction hobs, computer power supplies (which can be 1kw+ on gaming PCs) and high power battery chargers. All of which will work at freqencies far higher than the 20khz spec that Valliant is talking about. The trend is faster and faster switching speeds, cutting edge stuff will be working at 1Mhz+.

[JamesPa]

@-rick- you and I cross posted, I added a bit more detail, references and explanation, you may wish to re-read (or, more sensibly, you may not!)

 

And yes I agree that if an RCD is fitted it must be to the right spec.  I cant find the additional Vaillant requirements @sharpenerrefers to, the installation document still seems to say what mine said from 12 months ago..

 

I dont think you are missing anything.  The March document you referred to makes it very clear that the regs dont specifically call out heat pumps which sofaik are covered by the same regs as other external plant not specifically called out

 

Quote

4. Do the Wiring Regulations (BS 7671) have explicit requirements for heat pumps?

 

BS 7671 (IET Wiring Regulations) does not contain any specific requirements for the installation of RCDs for additional protection on a circuit for a heat pump. The additional requirements are intended for socket-outlets and mobile equipment for use outdoors, and under these circumstances do not apply. Selection of an RCD for a heat pump circuit therefore follows that for other electrical equipment and is covered in the current regulations

 

Edited 16 hours ago by JamesPa

[-rick-]

7 minutes ago, JamesPa said:

@-rick- you and I cross posted, I added a bit more detail, references and explanation, you may wish to re-read (or you may not!)

 

Below is a video with a discussion on this with Hager talking about how they worked with Valliant (at their request) to build something specifically for their heatpumps.

 

 

[JamesPa]

1 hour ago, -rick- said:

Below is a video with a discussion on this with Hager talking about how they worked with Valliant (at their request) to build something specifically for their heatpumps.

 

Can you tell us about where in time, 1hr 30 mins is a lot to go through.  I did see one with a natty heat pump symbol on 'to help plumbers', doubt that affects the electrical characteristics though.

Edited 15 hours ago by JamesPa

[-rick-]

4 minutes ago, JamesPa said:

Can you tell us about where in time, 1hr 30 mins is a lot to go through.  I did see one with a natty heat pump symbol on 'to help plumbers', doubt that affects the electrical characteristics though.

 

I haven't watched it all myself but the early bit covers most of it. Maybe ~8min - 18mins in. Watch at 2x speed to save time (though that takes a bit of getting used to

[HughF]

10 hours ago, sharpener said:

One last thing. Vaillant have recently changed the spec for the fancy RCD you will need, previously the cheap(ish) one from Fusebox was approved but now IIRC the only one is from Haager. This topic is a whole nightmare in itself.

Like that’s going to happen…. It’s getting whatever I’ve got spare in the drawer.