What to ask installers before upgrading to a hybrid heat pump and gas boiler system

Upgrading to a hybrid heat pump and gas boiler system can feel like a big step — and rightly so. I recently went through this process for my own home, and I learned that the key to a successful install isn’t just the equipment: it’s the conversation you have with your installer before any work starts. Below I share the practical, no-nonsense questions I asked and the things I wish I'd thought to check earlier. Use them as your checklist to avoid surprises, get the best-performing system for your house, and make sure the project actually saves you money and carbon in the long run.

Why ask questions? Start with objectives

Before you call an installer, be clear about what you want. For me, the main goals were to reduce gas consumption, keep comfortable temperatures without major radiator upgrades, and qualify for available grants. When you call an installer, open with your goals — reduction targets, budget range, and whether you want minimal disruption or are open to retrofit work. That frames the whole conversation and helps the installer propose options that fit you, not just what they want to sell.

Questions about installer credentials and experience

Experience matters. I asked every installer the same baseline questions and treated anything less than clear, documented answers as a red flag:

Ask to see proof — certificates, photos, and customer contact details. I prefer installers who can show full installations and who kept the same apprentice-teams on projects; it indicates consistent standards.

System design and sizing

One of the biggest mistakes I witnessed (and nearly made) was under-sizing the heat pump. Ask these questions and insist on seeing the math:

I asked for a written report showing heat loss calculations and an explanation of assumptions (insulation levels, occupancy patterns). If an installer can’t — or won’t — provide that, walk away. Proper sizing avoids cycling, noise issues, and excessive energy bills.

Controls, integration and smart features

Controls make or break a hybrid system’s efficiency. During my install, I insisted on smart controls and an explanation of how they would be configured:

A hybrid system that isn’t properly controlled can default to running the boiler more often than needed. I made sure the installer demonstrated the logic: heat pump first for lower-temperature space heating, boiler kicking in when quick top-up or very high flow temperature is needed.

Costs, savings and grants

Money talk is essential and I recommend getting all figures in writing:

Installers sometimes provide optimistic savings. I asked for a conservative estimate based on my bills from the past year and their projected fuel prices. That helped me feel comfortable that the upgrade was a good investment, not just an environmentally attractive one.

Warranties, guarantees and service plans

Warranty fine print matters. Don’t accept vague commitments:

I chose an installer who provided at least 5 years parts warranty on the heat pump and a clear route to rapid support. Poor aftercare turned out to be the main complaint among neighbours who’d had installs elsewhere.

Installation practicalities

Ask about the on-site experience — it’s your home, after all:

Get a schedule that includes milestones: delivery date, indoor works, outdoor unit placement, system commissioning, and final walkthrough. My installer left a clear test log and operational manual — a sign they cared about handover quality.

Performance, testing and commissioning

Don’t accept a handover without proof the system works as promised. Ask:

I watched the installer run through the modes and explained how to troubleshoot basic issues. Make them show you the app or control panel and set up any accounts or mobile access while they’re still on site.

Environmental and practical considerations

Some extra practical questions I found useful:

Noise and electrical upgrades are common unexpected costs. My installer flagged a weak consumer unit early and offered a quote for an upgrade which prevented lengthy delays during install.

Simple checklist table to take to appointments

I went into my upgrade armed with these questions and left with a system that performs and a team I trust. Treat your installer conversation as a partnership: the right questions will protect your wallet, your comfort, and the planet.