Large tank with two heat sources — heat pump plus gas boiler boost
The problem
A large storage tank is heated by two sources: a heat pump, efficient at low temperature, and a gas boiler that boosts to a higher one. The two sources must alternate in the right cycle — heat pump first, boiler after it — and work together when the tank is deeply cold. A ready-made panel with this logic practically does not exist.
Typical situations
- Domestic hot water for houses and small hotels with a heat pump and a gas boiler
- Buffer tanks in dual-source heating systems
- Retrofit: adding a heat pump to an existing gas installation
The ThermoB solution
One MTC5 with two tank sensors (T1 bottom — for the heat pump, T2 top — for the boiler) runs the whole cycle. When the tank cools to the start setpoint (e.g. 45°), relay R1 calls the heat pump; it runs up to its threshold (e.g. 50°) and switches off. That unlocks the boiler chain — a cell in the R2 row watches the heat pump relay state, so the gas boiler (R2) starts only after it and boosts to the upper setpoint (e.g. 65°). Then a pause follows until the tank cools back to 45°, and the cycle repeats. A separate parallel row engages both sources simultaneously at a very low temperature (e.g. below 40°) — fast recovery after heavy draw-off. All thresholds are user parameters with hysteresis, adjustable from the app without touching the logic.
Interconnection diagram
Products required
| Product | Quantity | Notes |
|---|---|---|
| ThermoB System · Proxel MTC5, Controller for heating, ventilation, air-conditioning and refrigeration installations — WiFi | 1 | Both sources on R1/R2, sequencing via a relay-state condition cell |
| Tank temperature sensors (bottom and top) | 2 |
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Optional products
| Product | Quantity | Notes |
|---|---|---|
| Circulation pump for the boiler loop | 1 | On a spare relay if the boiler has no own pump |
Compatible systems
Benefits
- The heat pump carries the base heating — cheapest energy first
- The gas boiler engages only to boost after the heat pump
- Both sources together when the tank is deeply cold
- The 45/50/65° thresholds are adjustable parameters with hysteresis
- Temperatures and the cycle monitored from the mobile app
Tell us what you want to control
Describe the machine or process. The controllers and the cloud platform are our own design, and support comes directly from the engineers who know the system.
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