Wireless Thermostats
OpenTherm Receiver (two zones)
In short
The OpenTherm receiver is the wall box of an OpenTherm two-zone set. Its terminals: E, L, N, COM1, ON1, COM2, ON2, OT1, OT2.
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What it is
The OPENTHERM RECEIVER is the wall box of an OpenTherm TWO-ZONE set. It has its own live (L) and neutral (N), two ZONE RELAYS, and an OPENTHERM pair to the boiler.
Each zone's wireless room unit tells it by radio when that zone calls. The zone's relay then makes, and feeds that zone's valve. And the receiver asks the boiler for heat over OpenTherm: in this simulator, the higher of the two zones' requests.
The relays are VOLT-FREE: they switch what you feed them. So link its L to COM1, and COM1 to COM2.
- Each relay's output goes to a wiring centre block, linked to its valve's brown.
- Both valves' oranges are parked on block 10, with nothing leaving it.
- The boiler has a permanent live, neutral and earth (L, N and E), and its OT pair.
DrawWarm's own design. Product and brand names belong to their owners; DrawWarm is not affiliated with any manufacturer.
Terminals
| Terminal | What it is for |
|---|---|
| E | The earth (E), from block 3: land it. The receiver is a control, and works without it. |
| L | The live (L) in, from block 1: the receiver's own supply. Link it on to COM1. |
| N | The neutral (N), from block 2. |
| COM1 | Printed COM under ZONE 1: zone 1's relay common (COM). It is VOLT-FREE, so link it from L. |
| ON1 | Printed ON: zone 1's output, live while zone 1 calls, with the links in. It goes to block 4, which is linked to the zone 1 valve's brown on block 5. |
| COM2 | Printed COM under ZONE 2: zone 2's relay common. Link it on from COM1. |
| ON2 | Printed ON: zone 2's output, live while zone 2 calls. It goes to block 6, which is linked to the zone 2 valve's brown on block 8. |
| OT1 | Printed OT: OpenTherm, to the boiler's OT terminal, either way round. It is EXTRA-LOW VOLTAGE: never 230 volts (230 V). |
| OT2 | Printed OT: the pair's other wire, to the boiler's other OT terminal. |
What the meter reads
Its live (L) to neutral (N): 230 volts (230 V). Its POWER light shows.
A zone turned up on its room unit: that zone's light shows, and its ON terminal is live, 230 V to N with the links in. The other zone's ON stays dead.
Isolated, a relay's common (COM) to its ON reads open (OL): the relays need the receiver's own supply.
Its OT light shows while it talks to an OpenTherm boiler. Across OT and OT, on volts: a low direct current (DC) voltage, about 5 V in this simulator. The specification allows 7 V at most. The other way round, it shows a minus sign.
Its screen shows OT LINKED, or OT 47°C, the flow it asks for. NO OT LINK means no boiler is talking on its pair.
Both zones satisfied: both ON terminals are dead, and the boiler is no longer asked for heat.
Where it connects
Lessons that use it
- Two zones on an OpenTherm receiver
Intermediate · Bus controls
Practise it in the simulator.
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