There are many legitimate reasons to criticise Britain’s heat pump rollout. Poor system design remains widespread, commissioning standards are inconsistent, homeowners are too often given inadequate guidance and, when things go wrong, the fragmented chain of installers, manufacturers, certification bodies and consumer protection schemes can leave people struggling to establish who is actually responsible. These are serious problems and they deserve serious journalism.
Unfortunately, a recent consumer column in The Daily Telegraph demonstrates another problem that is becoming increasingly difficult to ignore: some of the reporting intended to help consumers understand heat pumps is itself perpetuating the misconceptions that have helped create the confusion in the first place.
The article concerns a couple in Berkshire who paid around £25,000 for an air source heat pump installation and subsequently endured what appears to have been a thoroughly miserable experience when the system failed during winter. Their heating stopped working, attempts to obtain effective support dragged on, portable electric heaters had to be purchased and the household was reportedly left without central heating for weeks. One of the occupants subsequently became seriously ill with pneumonia. Whatever the precise technical circumstances, nobody should dismiss the distress caused when a household spends that amount of money on a new heating system only to find themselves without reliable heating in the depths of winter.
Yet woven through this entirely legitimate consumer complaint is a remarkable description of how the heat pump had been operated before it failed, and this is where the article begins to unravel.
The homeowner explains that the heat pump had been programmed to switch off overnight but appeared to ignore the timer, saying that it would “kick in” when it had not been programmed to come on and that “the heat pump was on almost all day and night”. The implication running through this section of the story is clear: a heating appliance operating for such long periods must surely be malfunctioning, wasting electricity or behaving in some inexplicable way.
Except a heat pump running for most of the day (and, under some conditions, most of the night) is not inherently evidence of a fault at all. Quite the opposite. It is the hallmark of a heat pump operating exactly as it was designed to operate: low, slow and continuous.
This distinction is important to make because a heat pump is fundamentally different from the gas or oil boiler most British homeowners have grown accustomed to using. A conventional boiler is frequently enormously oversized relative to the actual heat loss of the property. A house that might be losing 6kW of heat on a cold winter day could easily have a 24kW or 30+kW boiler attached to it, allowing the system to deliver relatively short bursts of very hot water through the radiators before switching off again. The house cools, the thermostat calls for heat and another large injection of energy follows. For decades, this stop-start pattern has conditioned homeowners to associate a heating appliance being “on” with substantial energy consumption and to assume that the longer it runs, the more expensive it must be.
A properly designed heat pump turns much of that logic on its head. Rather than producing enormous bursts of high-temperature heat, it should ideally operate at the lowest practical flow temperature, modulating its output and steadily replacing approximately the same amount of heat that the building is losing. As outdoor temperatures fall and the heat loss from the house increases, the heat pump naturally runs for longer. Around design conditions, a correctly sized system may operate almost continuously because that is precisely what it has been sized to do.
This is not some obscure theory promoted by heat pump enthusiasts. Heat pump training material has explained for years that these systems are not intended to behave like high-temperature boilers or rapidly reheat cold buildings. Even older industry guidance describes heat pumps as systems typically designed around a 24-hour heat-loss period, maintaining a comparatively steady temperature rather than repeatedly recovering a property after significant temperature setbacks. Modern low-temperature heating design follows the same basic physics: keep flow temperatures as low as practicable, allow the compressor to modulate and use appropriate manufacturer controls (typically weather compensation, load compensation or a combination) rather than repeatedly forcing the appliance through aggressive stop-start cycles.
That makes the concern about the heat pump running “almost all day and night” particularly revealing, because somebody should have explained this to the homeowners long before they became worried enough to contact the manufacturer. The installer should have explained the operating philosophy during handover, the controls should have been properly commissioned and the homeowners should have understood why a heat pump may continue operating for hours at a time without that necessarily translating into excessive electricity consumption.
There is, of course, an important qualification. If the homeowners explicitly programmed the heating to be off and the system continued delivering unwanted space heating regardless, there may indeed have been a control or commissioning problem that warranted investigation. Heat pumps can also operate outside apparent heating schedules for perfectly legitimate reasons: frost protection, domestic hot water production, defrost cycles and other control functions can all cause the outdoor unit to run when a homeowner might not expect it. The Telegraph article provides nowhere near enough technical information to establish what was actually happening.
What it does do, however, is leave the casual reader with the impression that a heat pump operating for most of the day is inherently suspicious. That is precisely the misconception we encounter repeatedly on the Renewable Heating Hub forums, where homeowners arrive after their first few weeks with a heat pump concerned that the outdoor unit “never switches off”. In many cases they have spent decades operating boilers on morning and evening schedules and instinctively attempt to impose the same regime on a technology that works most efficiently in a completely different way.
Indeed, programming a heat pump to shut down for several hours overnight can sometimes achieve the opposite of what the homeowner intends. During that setback period the building fabric cools, the emitters cool and the water circulating through the heating system cools. When heating resumes, the heat pump is no longer simply replacing the relatively modest heat being lost continuously from the building; it must also recover the temperature lost during the setback. Depending on the system and controls, that can mean higher compressor output, potentially higher flow temperatures and prolonged recovery periods… all of which can undermine the efficiency supposedly gained by switching the heating off.
This is the essence of the often-used phrase “low and slow”, although the phrase itself can oversimplify what is actually happening. The objective is not to run a heat pump continuously for the sake of it, nor is continuous operation automatically proof of good performance. The objective is to allow the system to deliver the required amount of heat at the lowest practical water temperature and compressor output, modulating as closely as possible to the changing heat loss of the building. A heat pump drawing relatively modest electrical power while running steadily for many hours can be operating extremely efficiently, while another system cycling repeatedly, ramping its compressor and producing unnecessarily hot water may run for fewer hours but consume considerably more electricity.
Runtime, in isolation, tells us almost nothing about whether a heat pump is performing well.
Then we come to the glycol.
According to the article, when the heat pump stopped working the manufacturer advised that the system needed glycol, after which the system was drained and a technician reportedly added more glycol before the heat pump began working again. Once again, there may be a perfectly rational technical explanation for what happened, but the article does not provide enough information to establish one. Instead, the addition of glycol appears almost as a routine remedy… the heating equivalent of discovering that the windscreen washer bottle is empty and topping it up.
Glycol is not something that should simply be poured into a heat pump system until the appliance starts working again. In fact, most top installers will tell you modern heat pump systems don’t need glycol.
If glycol freeze protection was required by the manufacturer, the correct concentration should have been specified, installed, tested and documented when the system was commissioned. If glycol was already present, the obvious questions are what concentration was measured, whether it was actually below the required freeze-protection level, why that had happened and whether the system had been hydraulically designed to operate with the resulting glycol mixture. None of those questions appears to have been explored.
This is crucial because adding glycol changes the physical characteristics of the fluid circulating through the heating system. Compared with plain water, glycol mixtures generally have greater viscosity and different heat-transfer characteristics, which can increase hydraulic resistance and alter the flow required to transport a given amount of heat. Low-temperature hydronic training material specifically warns that systems containing glycol may require additional pumping allowance compared with water-based systems, particularly as concentration increases and temperatures fall.
That does not mean glycol should never be used. Some manufacturers require particular forms of freeze protection and there are installations where glycol is an entirely legitimate engineering choice. The point is that its concentration and hydraulic consequences should form part of the system design, not appear halfway through a newspaper story as an unexplained magic liquid that apparently restores a failed heat pump to life.
The tragedy is that beneath all this confusion there is a genuinely important consumer story that deserved much deeper investigation. A household reportedly spent around £25,000 on a new heating system, suffered a serious winter failure, struggled to obtain timely support and was left relying on portable heaters while responsibility apparently bounced around between different parties. Those circumstances raise legitimate questions about installation quality, commissioning, warranty obligations, manufacturer support, servicing arrangements and what happens when a homeowner discovers that the supposedly joined-up consumer protection surrounding a heat pump installation is anything but joined up.
Instead, genuine service failures become muddled together with what may have been entirely normal heat pump behaviour. A reader unfamiliar with the technology can therefore emerge from the article with a rather predictable collection of impressions: heat pumps run uncontrollably day and night, ignore timers, mysteriously require extra glycol and can leave homeowners freezing when something goes wrong.
Is it any wonder public confidence remains fragile?
For years, the national debate has been framed around the simplistic question of whether heat pumps “work”. It is increasingly obvious that this is the wrong question. Heat pumps work perfectly well (the vapour-compression cycle is hardly experimental technology) but their success in an individual home depends enormously on how the complete heating system is designed, installed, commissioned, controlled and subsequently explained to the person who has paid for it.
A good heat pump installation is not simply an outdoor unit connected to some existing pipes. It requires an accurate understanding of the building’s heat loss, appropriate heat pump sizing, correctly sized emitters, sufficient water flow, sensible hydraulics, appropriately low design temperatures, effective weather or load compensation, correct commissioning and suitable freeze protection. Just as importantly, it requires a homeowner who has been shown how their new heating system differs from the boiler it replaced and why behaviours that would have seemed alarming with a 30kW gas boiler may be completely normal with a modulating heat pump.
If somebody can spend £25,000 on a heat pump installation and subsequently become alarmed because it runs for most of a winter day, something has already failed, even if the heat pump itself has not. The homeowner has not been properly prepared for the technology they have bought.
That failure of communication is bad enough at installation level. When the same misunderstanding then passes through the editorial process of one of Britain’s largest newspapers without being properly challenged or contextualised, the damage becomes much wider. Hundreds of thousands of readers can have an existing suspicion confirmed by an apparently authoritative consumer column: heat pumps run all the time, therefore heat pumps must be expensive, uncontrollable or fundamentally unsuitable for British homes.
There is no shortage of genuine heat pump failures for journalists to investigate. Poor heat-loss calculations, oversized and undersized units, inappropriate buffer tanks and hydraulic separation, inadequate pipework, excessive flow temperatures, badly configured controls, questionable glycol practices, weak commissioning and atrocious aftercare are all real problems. Renewable Heating Hub encounters homeowners dealing with these issues every week, and the industry deserves intense scrutiny for allowing so many of them to persist.
But scrutiny has to be technically literate if it is going to help consumers.
The Berkshire couple featured in the Telegraph article deserved a reliable heating system and far better support when it failed. They also deserved, from the day it was commissioned, a clear explanation of how their £25,000 heating system was supposed to operate.
And readers of a national newspaper deserved the same basic explanation before being invited to regard a heat pump running for most of the day as part of the problem.
Because Britain undoubtedly has a heat pump problem.
But sometimes the problem is not the heat pump.
It is what people are being told about it.
