Are heat pumps worth it? Only if you stop running it like a boiler

Are heat pumps worth it? Usually, yes. But the honest answer depends on what you’re replacing, and more than that, on how you actually run the thing once it’s in.

I fitted one in Sittingbourne last winter for a family coming off an old back boiler. Sensible house, decent radiators, nothing unusual about the job. Six weeks later I got a call. The bills were higher than the boiler had ever cost, and they wanted to know if they’d been sold a lie.

They hadn’t been sold a lie. They’d been running a heat pump like a boiler, because that’s the only way anyone had ever heated a house before. Off in the morning, blast it hot when you’re cold, off again at night. A boiler doesn’t mind that. It fires up, gets the water scalding, and shuts off happy. A heat pump hates it. Ask it for a high flow temperature in one go and it works about as hard, and about as inefficiently, as an immersion heater.

Turn the same heat pump down to a low, steady flow temperature and leave it running gently through the day, and it’s a different appliance. Same box on the wall, same radiators, half the running cost. Once we changed the settings and stopped fighting the thermostat twice a day, their bills came in under what the old boiler had cost them.

So the real question isn’t “are heat pumps worth it”. It’s whether you’ll let it run the way it wants to run. Most of the disappointment I get called out to fix isn’t a broken heat pump. It’s one set up like a boiler by an installer in a hurry, or nudged back that way by someone who got cold one evening and cranked the flow temperature up for a quick blast of heat.

There’s a cost side too, and I won’t pretend it away. A heat pump costs more to install than a boiler, even with the £7,500 Boiler Upgrade Scheme grant knocking a chunk off. If your existing boiler is five years old and running fine, I’d tell you to wait. Replacing a healthy boiler with a heat pump just to be green is usually the wrong call financially, whatever the adverts say. But if your boiler’s on its last legs and due for replacement anyway, the sums change completely, because you’re comparing the price of two new systems, not old against new.

What actually decides whether it’s worth it, more than the grant or the install cost, is whether you or your installer are willing to leave the thing alone. Weather compensation, a sensible target flow temperature, and the patience not to fiddle with it every cold snap. That’s the whole trick. I’ve seen a fifteen-year-old semi near Ashford run cheaper on a heat pump than the boiler it replaced, and a newer house down the road struggle, purely because one owner trusted the system and the other kept overriding it.

If you’re weighing it up, ask whoever quotes you how they’ll set the flow temperature, not just what the unit costs. That one question tells you more about your future bills than any spec sheet, and it’s most of what separates a good heat pump installation from a gas boiler replacement dressed up as one.

I still fit boilers. Sometimes that’s the right answer for that house, that week, that budget. But when people ask me if heat pumps are worth it, I tell them the truth: yes, almost always, just not if you insist on running it like the boiler it replaced.