Behind the Scenes: Fixing a Real Heat Pump System
- Leah Robson
- 5 days ago
- 4 min read
We recently had the opportunity to work on a real home, with real challenges, alongside a homeowner who has been very publicly sharing her journey: Judith Leary-Joyce.
If you haven’t already, you can watch the full Everything Electric episode here:
And we strongly recommend reading Judith’s own write-up of her experience: https://www.ecorenovationhome.com/post/i-m-learning-about-heat-pumps-the-hard-way-now-you-don-t-have-to
This is the behind-the-scenes version of what went wrong, what we found on site, and what we changed.
The Reality: It Wasn’t the Heat Pump
There’s a lot of noise around heat pumps right now - strong opinions, frustration, and in some cases, genuinely poor experiences.
But in Judith’s case (and in many others we see), the heat pump itself wasn’t the problem.
There were two core issues:
System design and setup
How the system was being used
Fix those, and everything changes.
What We Found on Site
When we arrived, the system had been set up in a way that’s very common - but not optimised for a heat pump.
1. Too Many Pumps
There were multiple circulating pumps:
One on the primary pipework
One connected to the buffer
One on the underfloor heating manifold
For a house of this size, this is unnecessary.
What this does in practice:
Adds electrical consumption
Increases system complexity
Creates more points of failure
Makes system behaviour harder to predict
A well-designed heat pump system should be simple and hydraulically balanced. Extra pumps often create more problems than they solve.
2. Thermostats Fighting the System
The system was being controlled by a Nest thermostat.
This is designed for gas boilers, not heat pumps.
Here’s the issue: As the room temperature approaches the target, the thermostat starts cycling the heat source on and off. That behaviour works for boilers, but for heat pumps it creates inefficiency and wear, which is known as short cycling.
Heat pumps work best when they are allowed to run continuously at low output.
3. Running It Like a Boiler
This is the big one.
The system had been operated in a traditional “on/off” way, with zoning and selective heating.
That approach:
Forces higher flow temperatures
Reduces efficiency
Creates uneven comfort
Heat pumps are designed to run differently.
The Oversizing Question (And the Real Problem)
A lot of people worry about oversizing heat pumps, and rightly so. But it’s important to be clear about where the real impact sits. If you overestimate heat loss, you will often end up installing larger emitters (radiators or underfloor loops) than you actually need.
That’s the main issue.
Larger emitters are more expensive
They take up more space
And in many cases, they’re simply unnecessary
From a practical point of view, that’s where most of the downside of oversizing shows up.
There is also the question of minimum modulation.
Heat pumps can turn down their output, but not to zero. If a system is significantly oversized, it may reach temperature quickly and begin cycling.
Most modern heat pumps have good modulation ranges, and the best units are very capable of turning down effectively.
Oversizing can:
Reduce efficiency slightly
Increase wear and tear over time.
The real issue is that some people don’t install a heat pump because they get told to change too many radiators, making the heat pump too expensive and disruptive.
Some people suggested using “silent mode” on the YouTube comments - while this reduces fan and compressor speed, it does not change the fundamental minimum output range of the heat pump - so it’s not a real fix for oversizing.
In short: oversizing isn’t ideal, but the biggest real-world consequence is unnecessary emitter cost, and not catastrophic system performance.
What We Changed
1. Simplified the System
We began removing unnecessary complexity:
Reducing the number of pumps
Planning removal of redundant components
The goal is always the same: simpler systems perform better.
2. Reintroducing Radiators
Two radiators had been removed because they were rarely used.
But for a heat pump, emitter area matters.
We reinstated them to:
Improve heat distribution
Allow lower flow temperatures
Support continuous operation
3. Switching to “Low and Slow”
This is the biggest mindset shift.
Instead of: High temperatures and intermittent heating
We moved to:
~40°C flow temperature
All emitters on
System running continuously
The result? More stable temperatures, better comfort and higher efficiency.
Judith described it best: warmer house, with less awareness of the heating system at all.
4. Upgrading the Controls
We removed the Nest thermostat.
In its place, we are moving towards a Homely system.
Why this matters:
Homely is designed specifically for heat pumps
It learns how the home heats and cools
It adjusts the flow temperature dynamically
Reduces cycling
Improves overall efficiency
It also gives us visibility into system behaviour, so we can spot issues like short cycling early.
The Bigger Lesson
Judith’s experience highlights something important.
When heat pumps don’t perform, it’s usually not because the technology doesn’t work.
It’s because of:
The system wasn’t designed properly
The controls aren’t suitable
The way it’s being used hasn’t been adapted
Fix those three things, and the difference is dramatic.
Final Thoughts
There is a lot of misinformation around heat pumps, but real homes, properly set up, tell a different story.
This project is a great example of what happens when you strip things back, simplify the system, and run it the way it was designed to operate.
If you’re struggling with your heat pump, it’s worth questioning the setup before blaming the technology. In most cases, the fix is there - it just needs someone who knows what to look for.
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