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Surge Protection Devices

trebor12345 · 2026-02-20T16:26:11Z

This Topic has been changed by the Moderators in order to address only the fitting of Surge Protection Devices (SPDs) to consumer units. The Original Post, which follows here, concerned the type of protection device which supplied a heat pump.That portion of the discussion has been deleted as it gave incorrect information on the subject of electrical safety devices. I am having my existing heat pump changed to a Vaillant (another story). The question of fuse type has come up in conversations. According to the Vaillant spec I need this: The current fuse I have is this: Is this the right one?

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Air Source Heat Pumps (ASHPs)

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trebor12345

(@trebor12345)

Estimable Member Member

Joined: 2 years ago

Posts: 160

Topic starter 11/06/2026 8:21 am

In my recent Vaillant install I had some lengthy discussions with my installer as to why I needed another consumer unit and this special RCCB from Hager. I gave in at the end. Added over £600 to my install costs.

2024 build bungalow, Southern England, 179 m2, 14w/m2
Underfloor heating, fully open
Vaillant aroTHERM plus 3.5kW
50 litre volumiser
3.6KW solar panels

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 4993

11/06/2026 8:47 am

What was the reason given. You don't even need an RCD for external fixed plant, an MCB will suffice (although an RCD is certainly to be preferred).

This post was modified 1 hour ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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trebor12345

(@trebor12345)

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Posts: 160

Topic starter 11/06/2026 8:57 am

Posted by: @jamespa

↑

What was the reason given. You don't even need an RCD for external fixed plant, an MCB will suffice (although an RCD is certainly to be preferred).

Manufacturers requirement.

2024 build bungalow, Southern England, 179 m2, 14w/m2
Underfloor heating, fully open
Vaillant aroTHERM plus 3.5kW
50 litre volumiser
3.6KW solar panels

ReplyQuote

Batpred

(@batpred)

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Joined: 1 year ago

Posts: 989

11/06/2026 9:25 am

@jamespa

Vaillant have specific requirements in term of RCD type and MCB curve. Contactum sell these types of RCBOs in 16A for £25 (in boxes of 5).

I am yet to see information from Vaillant requiring a specific brand of CU, but the supposed requirement is one of those that some sparkies do not forget. Also some add an SPD for good measure. 😀 Why not, anyone getting a heat pump must have cash to spare? 😉

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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JamesPa

(@jamespa)

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Joined: 3 years ago

Posts: 4993

11/06/2026 9:32 am

Posted by: @batpred

↑

Vaillant have specific requirements in term of RCD type and MCB curve. Contactum sell these types of RCBOs in 16A for £25 (in boxes of 5).

@trebor12345 @batpred

My version of the Vaillant installation manual, from about 2 years ago, has specific requirements for RCD type if an RCD is specified for the installation (which is fair enough). However it does not require that an RCD is specified for the installation and neither does the IET regs (which is also fair enough). I looked online last about 6 months ago and the wording had not changed. Maybe it has subsequently changed.

This post was modified 31 minutes ago by JamesPa

This post was modified 30 minutes ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Batpred

(@batpred)

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Joined: 1 year ago

Posts: 989

11/06/2026 9:45 am

@jamespa

I fear the average installer will not question it. The way it was explained to me is that it is required by Vaillant for the warranty. But then the detail was that there is an inverter inside the Arotherm and if faulty, it can push out DC currents.

I would expect that, in that casem the protection would be for the rest of the installation to not get DC from a faulty heatpump. So how could this have an impact on the Vaillant warranty I cannot understand..

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 4993

11/06/2026 9:46 am

Posted by: @batpred

↑

@jamespa

I would expect that, in that casem the protection would be for the rest of the installation to not get DC from a faulty heatpump. So how could this have an impact on the Vaillant warranty I cannot understand..

The first question to ask is, does it? What does the latest Vaillant Installation manual actually say? Bear in mind that some tradesmen speak out of the wrong part of their anatomy!

This post was modified 18 minutes ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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trebor12345

(@trebor12345)

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Joined: 2 years ago

Posts: 160

Topic starter 11/06/2026 9:54 am

Posted by: @jamespa

↑

Posted by: @batpred

↑

Vaillant have specific requirements in term of RCD type and MCB curve. Contactum sell these types of RCBOs in 16A for £25 (in boxes of 5).

@trebor12345 @batpred

My version of the Vaillant installation manual, from about 2 years ago, has specific requirements for RCD type if an RCD is specified for the installation (which is fair enough). However it does not require that an RCD is specified for the installation and neither does the IET regs (which is also fair enough). I looked online last about 6 months ago and the wording had not changed. Maybe it has subsequently changed.

The requirement for me came from the following document.

2024 build bungalow, Southern England, 179 m2, 14w/m2
Underfloor heating, fully open
Vaillant aroTHERM plus 3.5kW
50 litre volumiser
3.6KW solar panels

ReplyQuote