Poor Heating Performance When Running Only on Cheap Tariffs

Trying to Run a Heat Pump Only on Cheap Tariffs – Poor Comfort & Inefficiency

System Type: Air Source Heat Pump Valiant

Issue Type: Control Strategy / Efficiency / Comfort

The Problem

A homeowner was trying to reduce running costs by only heating the house during off-peak electricity periods.

The system was set to run during three “cheap rate” windows, with the heating off for the rest of the day.

In reality, the house wasn’t maintaining a consistent temperature, and comfort levels were poor.

What I Found

The issue wasn’t the heat pump itself — it was how it was being used.

Heat pumps aren’t designed to heat a house in short bursts like a traditional boiler. By restricting operation to a few time periods:

• The house was cooling down too much between cycles

• The system had to work harder to recover temperature

• Efficiency was reduced due to higher required flow temperatures

On top of that, the system hadn’t been properly set up with weather compensation aligned to the property.

What I Changed

After some discussion, I advised a different approach:

• Set the heating to run continuously during the day at 20°C

• Introduced a small night setback to 18°C

• Configured weather compensation properly:

  • 44°C flow at 0°C outside

  • 35°C flow at 18°C outside

This allowed the system to run steadily, rather than constantly starting and stopping.

The Outcome

Once set up correctly, the system ran continuously at a low level, maintaining a stable indoor temperature throughout the day.

The homeowner reported:

• Much improved comfort

• No need to constantly adjust settings

• A more stable and predictable system

Over a 6-month period, the setup worked consistently without further changes.