Boiler Replacement
Although the government is trying to encourage the adoption of heat pumps, many people aren't ready to replace their entire heating system yet. A cheaper and less disruptive option is to replace the gas boiler with a modern, high-efficiency one.
Best-in-class condensing gas boilers can achieve 90% efficiency. This means 90% of the energy in the supplied gas in converted to useful heat energy. Older boilers typically operate well below these levels, with an average 25 year old boiler achieving as little as 60% efficiency. In this situation you could reduce your gas usage by a third by upgrading. A new boiler might cost £2000-3000, but with current high energy prices the upgrade could pay for itself in a few years, especially if you're heating a larger property.
Some manufacturers now offer ‘hybrid’ boilers which connect to a heat pump but also burn gas. These are intended to operates as a heat pump, but with gas power in reserve to top up the power if the heat pump proves insufficient to heat the home properly. This may be appealing to those with larger or less well-insulated properties, but in these instances perhaps adding insulation would be the more cost-effective approach.