Why does my hybrid system cost more and lack the expected thermostat setting?

Match the sale to the installation

Gather the proposal, invoices, thermostat model, indoor and outdoor labels, and handover instructions. Ask the installer to identify every heat source and how the controls select between them.

A missing feature does not alone prove incorrect installation. Google states that Nest Heat Pump Balance is not used with dual-fuel systems. A gas-backup arrangement may use a different setup. Google control guidance.

Have the provider confirm compatibility and wiring. Do not move wires or copy another system's configuration.

Ask for startup evidence

Request documented checks showing that each heat source operated and the controls selected it correctly. PNNL identifies control verification as part of commissioning, the checks after installation to confirm operation. PNNL commissioning guidance.

Ask about any temperature-based changeover and who may adjust it. Settings should fit the equipment, heating need, and intended cost strategy.

If the arrangement differs from the written proposal, request an explanation and options for resolving that difference.

Compare the whole bill

Gather gas and electricity use, billing dates, tariffs, schedule, and weather. If gas equipment remains, include continuing fixed gas charges.

Ask whether the increase reflects rates, weather, backup use, settings, or a confirmed fault. One month's result is a reason to investigate, not proof that all hybrid systems cost more.

Your next step is an installer review of equipment, controls, startup evidence, and total household energy. Request findings and corrections in writing. The useful result is a system you understand, with a reason for how it selects its heat source.