i just mean dc in the wire

But my angle was actually on whether an RCD could be justified solely based on the likely DC components?

No.

The shape of the waveform has no bearing on the decision to use an RCD.

BTW. I'm still unsure why you're making "DC Component" into a plural.
Could you give an example for me please?

So would the presence of DC components require RCDs to be fit?

Erm... I can interpret that question in more than one way, so I'm unsure of the angle you're taking.

All Type-B RCDs and RCBOs will correctly trip ii there is an element of Direct Current superimposed onto the mains 50Hz waveform.
I've deliberately changed the wording to clarify the concept.

The reasons that earth-leakage devices are fitted to circuits is usually to

• protect the cable in the event of fire / over-heating
• prevent death in the unlikely event of a person touching a live wire or connector
• prevent the metal casing on an appliance becoming live due to a short-circuit fault

That decision is the same irrespective of whatever aberrations are present on the sine wave.

In the case of our installation site, I see value in having the RCD fit, so we will have it. In many other cases, since I understand isolators are typically installed near the heatpump (EST guidance), unless the RCD would remove the need for such isolator, it seems to mostly add to costs without significant value.  

But my angle was actually on whether an RCD could be justified solely based on the likely DC components?

So would the presence of DC components require RCDs to be fit?

Erm... I can interpret that question in more than one way, so I'm unsure of the angle you're taking.

All Type-B RCDs and RCBOs will correctly trip if there is an element of Direct Current superimposed onto the mains 50Hz waveform.
I've deliberately changed the wording to clarify the concept.

The reasons that earth-leakage devices are fitted to circuits is usually to

• protect the cable in the event of fire / over-heating
• prevent death in the unlikely event of a person touching a live wire or connector
• prevent the metal casing on an appliance becoming live due to a short-circuit fault

That decision is the same irrespective of whatever aberrations are present on the sine wave.

Harmonics:

Are heat pumps inherently a major contributor to these losses? If that is the case, Germany and the Nordics would be having a big problem?

I haven't communicated with grid engineers in countries outside Britain.

Nor have I investigated whether their certification requires lower levels of harmonics to be emitted by heat-pumps than we allow in GB.

We already have an excessive amount of regulation for our electrical installations and appliances.
I don't think we've benefited as a result.

As an example, companies who install heat-pumps must be signed up to the RECC (Retail Energy Code).
That's a digital library which pulls together all governance issues which were previously published by other organisations.

But would you know if actions taken by a heat-pump installer complied with RECC requirements?

If your heat-pump, storage battery or solar inverter were intermittently ceasing to work, do you know where you'd look in the RECC documentation to find who's responsible?

How could you discover if those faults were being instigated by harmonics?

We've spent £millions creating The RECC, but it lacks the cross-indexing which would make it functionally useful.

Perhaps I'm the only one here who has attempted to consult the RECC on a real-world issue.

Could it be that Vito's arguably excessive focus on these perceived risks is making all installations more expensive than Vaillant anticipated? 

Yes, and doubtless, as @transparent observed, more profitable.

My installer somewhat cannily circumvented the whole issue by asking me if I was willing to get the circuit put in before he arrived.  So he was presented with a signed off 16A circuit (actually capable of 32A in case needed in future, but deliberately down-fused) certified by a qualified electrician to be compliant with regs, with a breaker on the end to which the installer could make a connection.  It meant I had to pay VAT on the installation of the circuit, but at sub £200 (I did first fix myself) that really didn't matter a whole lot.  My 'second choice' installer was proposing to take the exact same approach. 

I do realise that this is an unusual route which few would take, helped by the fact that I have worked with the electrician in question for a decade and he is one of those relatively rare tradesmen that you can just trust to do the right, but not excessive, thing.

And not knowing for sure if the DC leakage is solved,

The issue isn't DC leakage.

Type-B RCDs and RCBOs will trip correctly despite the waveform having a DC component present.

So would the presence of DC components require RCDs to be fit? Vaillant does not seem to be different from other heat pump manufacturers: they state that local regulations would determine such need.   

I've created the above timeline from spreadsheet date sent to me by a DNO.

It shows the absolute deviation of voltage imbalances which are being passed through local substations and on to the higher voltages of the Distribution Grid (11kV and above).

Whilst losses due to phase imbalances are substantially occurring only at the local substation level, harmonics pass right through every transformer on the grid. This is what causes the audible hum when you're in the vicinity of larger transformers. That's energy being lost.

Are heat pumps inherently a major contributor to these losses? If that is the case, Germany and the Nordics would be having a big problem?

Vito Energy has information on their website about this Hager/Vaillant collaboration. Hager still shows some info in their website. 

Could it be that Vito's arguably excessive focus on these perceived risks is making all installations more expensive than Vaillant anticipated? 

I can see no functional advantage in a heat-pump being supplied via an RCD.

It's purely a protective device, and won't operate at all unless there is a certain type of fault.

What am I missing?

The additional profit being made the installers. 

I am not missing that, I assure you!

I am trying (and failing) to find in Vailant's documentation, the underpinning for your statement:

It seems odd to me that Vaillant have introduced an AC to DC power supply into their ASHPs which is imposing both errors onto the mains incomer to sufficient extent that the company has teamed up with Hager to recommend a particular protection trip.

...

Consumers shouldn't be asked to spend £600 having an expensive RCD fitted just because the heat-pump power supply has design deficiencies.

I reiterate that, whilst I agree with your final sentence, neither my Vaillant documentation, nor the document @trebor12345 produced, appears to require an RCD at all.  So where exactly in the Vaillant documentation do you believe it say this?  Just because some potentially self motivated (as you rightly point out) installer says something is the case does not mean that it is the case!