Sometimes it happens that with a certain type, often older, on/off boiler (or pump / valve / gas block) the boiler always remains on.

The Adam and Anna (24V version) switch a 24V on/off thermostat input from the boiler by making the resistance low (about 2k ohms), or very high (about 200k ohms). This is inherent to the design of the circuit because on/off and OpenTherm can be communicated on the same connection. Because Adam and Anna can control both OpenTherm and potential free on/off on the same contacts, an off signal is to increase the resistance. An old thermostat that did work on the boiler probably had a relay that breaks contact completely.

Possible solutions:

- The boiler needs an anticipation resistor. Check the connections in the installation manual. For example, it may be possible that there are three connections for the thermostat and that an anticipation resistor must be placed there. The resistance differs per boiler how high it should be.

Example with ATAG boiler that needs 220 ohm/5WL

- You have a 230V thermostat input on the boiler. If you have connected Adam and Anna (24V version) to this, they have broken due to the much too high voltage. To still be able to control your boiler, you must use the Anna 230V.

Haven't connected the Adam or Anna (24V version) yet? You can then still connect it to your boiler by using a relay. Connect Adam/Anna (24V version) to the relay with an additional power supply. You can buy this relay in our webshop:

You can also make your own relay box. A relay needs a power supply because Adam/Anna does not supply it through the boiler wires. For example, you can use a USB power supply that outputs 5V as a power supply. Cut off the USB plug and strip the wires. Example of a circuit with relay and power supply: