Technical Note: Thermino xPlus in back-up Electric Mode

(D0093)

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1. Introduction

1.1 General

The following instructions provide guidance for the installer and end-user of Thermino® xPlus heat batteries when used in back-up electric mode (charging via the internal heating element).

The installation of Thermino® xPlus in back-up electric mode must be carried out by a competent installer in accordance with local codes and regulations for plumbing, electrical installations and potable water supply.

Please note that using a Thermino® xPlus in back-up electric mode is not the standard intended use of the product. The primary function of a Thermino® xPlus heat battery is to be hydraulically charged by an external heat source (i.e. Heat Pump or Boiler) as a primary source of energy. This options requires the use of an appropriate Optimino® key from the XX01 range. For detailed information on standard installation of the heat battery, please refer to document D0101.

The installation of Thermino® xPlus heat batteries in continuous back-up electric mode is a temporary solution and will only be permitted in the circumstances highlighted below. Otherwise, it will be considered a non-standard installation as it deviates from the intended use of the product, which will invalidate the manufacturer’s warranty:

• The Heat Pump or Boiler is momentarily non-operational due to maintenance requirements.

• The Heat Pump or Boiler is not operational in DHW mode only.

• For DSR services.

To operate Thermino xPlus heat batteries in temporary continuous electric mode, please refer to document D0116.

1.2 Symbols Used

1.3 Abbreviations

The following abbreviations are used throughout the document:

• DHW – Domestic Hot Water

• DSR – Demand Side Response

• MCB - Miniature Circuit Breaker

• PDC – Power Diversion Controller

• PV – Photovoltaic

2. Safety

2.1 General Safety Notices

CAUTION

Each heat battery must be protected by its own dedicated MCB and have a double pole isolating switch with a contact separation of at least 3mm in both poles, which is located in close proximity to the heat battery. For required MCB specification, please refer to Table 1 of the heat battery installation and user instructions manual.

CAUTION

Use the strain reliefs supplied with the heat battery to ensure cables are secured in place.

3.0 Accessing Back-up Electric Mode

Accessing back-up electric mode in Thermino® xPlus heat batteries can be achieved by following the installation procedure outlined below. Please follow these instructions in conjunction with the Thermino® xPlus manual (document D0101) for the correct installation and commissioning of the product.

NOTICE

Note that using Thermino® xPlus heat batteries in back-up electric mode is not the intended use of the product. Please be aware that this may affect the energy efficiency of the product. Therefore, extended use of Thermino® xPlus heat batteries in back-up electric mode is not recommended and is restricted to the circumstances listed in the Introduction.

NOTICE

Engaging the Volt-Free switch below will put the heat battery into electric back-up mode. This can lead to increased electricity consumption, resulting in higher energy costs. This should be explained to the end user and the switch labelled accordingly.
Do not remove the Optimino key.

3.1 Installation of a Volt-Free Switch

WARNING

Risk of electric shock – potential dual supply. Always isolate the power supply/ies to the heat battery controller before working on the heat battery.

Fit a VOLT-FREE switch on the charge link between terminals 1 & 2 in the controller wiring centre. Closing this switch will force the unit into back-up electric mode. Please note, it is not recommended to programme scheduled reheat times once a Thermino xPlus product is connected to an external heat source as this might lead to increased grid electricity consumption. Please refer to Figure 1 below:

Figure 1: setting Thermino xPlus in back-up electric mode by installing a Volt-Free switch

You can alternate between ‘external heat source charging mode’ and ‘internal heating element (electric) charging mode’ by closing & opening this switch.

‘internal heating element (electric) charging mode’ = Switch closed (ON).

‘external heat source charging mode’ = Switch open (OFF).

NOTICE

If an external heat source is installed and operational, every time back-up electric mode is activated, the unit will experience a 5-minute timer between external to internal heat source switchover to avoid simultaneous heat source operation. This protects the heat battery and external heat source from overheating.

NOTICE

For detailed wiring, hydraulic installation and commissioning instructions, please refer to the heat battery Installation & User Instructions manual.

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Document Part Number: D0093

Version Number: 1.0

Publication Date: 02.02.2026