Background

A 1930s detached property in Hampshire had installed a hybrid system combining an air source heat pump with an existing gas boiler. The homeowner observed excessive gas usage even during mild outdoor conditions.

Property & System Overview

• Property: Detached 1930s home

• System: Hybrid ASHP + Gas Boiler

• Control Strategy: Bivalent configuration

• Observed Issue: Boiler activating prematurely

Initial Observations

Hybrid systems require precise control sequencing. If the switching logic between heat pump and boiler is not configured correctly, efficiency can drop significantly.

Technical Findings

We identified:

1. Incorrect Bivalent Point Setting
   The boiler was programmed to engage at higher outdoor temperatures than necessary.

2. Overlapping Control Logic
   The heat pump and boiler were not sequenced correctly, leading to unnecessary boiler operation.

3. Flow Temperature Conflict
   Boiler settings were influencing system temperature behaviour.

Impact on Performance

The result was:

• Unnecessary gas consumption

• Reduced renewable contribution

• Increased total energy costs

• Reduced system optimisation

Corrective Strategy

• Reconfigure bivalent switching point

• Adjust control logic sequencing

• Optimise heat pump priority during moderate temperatures

Outcome

After adjustment:

• Boiler runtime reduced significantly

• Gas consumption lowered

• Renewable usage increased

• Comfort levels maintained

The system operated more in line with intended hybrid design principles.