No Heating Or Hot Water? The Heat Pump Was Fine – The Leak Was Hidden Inside The Wall

No Heating Or Hot Water? The Heat Pump Was Fine – The Leak Was Hidden Inside The Wall

The Problem

A homeowner got in touch after losing both heating and hot water at their property. The system appeared to be running normally, the outdoor unit was active, and there were no fault codes displayed anywhere on the controller. Despite this, the hot water temperature was dropping unusually fast after every heating cycle, and the heating was failing to keep the property comfortable.

The homeowner had already concluded that the heat pump itself must have a fault and was worried about the potential cost of a repair visit, replacement components, or something more serious.

Rather than arranging an engineer site visit, we offered a remote video consultation to review the system properly before drawing any conclusions about what might need doing.

What We Found

During the video call, we watched the heat pump start a domestic hot water cycle in real time. The cylinder temperature began climbing steadily on the controller display, exactly as it should. The cycle completed normally and the system transitioned from hot water mode to space heating, which also appeared correct.

At that point, there was nothing on screen that indicated a fault of any kind. The heat pump was behaving exactly as a correctly functioning system should behave.

Then, a few minutes after the hot water cycle completed, the homeowner checked the cylinder temperature again.

It had already dropped noticeably, and no hot water had been drawn at any tap, shower, or outlet anywhere in the property.

That detail was the critical indicator. A cylinder loses temperature slowly through its insulation over hours, not in minutes. What we were seeing was something actively carrying heat away, which pointed clearly to stored hot water escaping from the system somewhere.

If no hot water was being drawn, but the cylinder temperature was falling rapidly, water was leaving the system and the question was where.

This gave us a clear diagnostic direction to pursue.

Further Investigation

To test the theory, we asked the homeowner to slowly close the main hot water outlet valve from the cylinder, which is the valve that controls all flow from the cylinder into the property’s hot water distribution pipes.

As the valve was progressively closed, the homeowner could clearly hear water continuing to move rapidly through the pipework.

That confirmed the diagnosis. Closing that valve should have significantly reduced or stopped all hot water movement downstream. The continued sound of flowing water meant water was escaping actively somewhere beyond the valve through a break in the pipework that the heat pump had no way to detect.

The heat pump had been working exactly as intended throughout. It heated water, filled the cylinder to its target temperature, and completed the cycle normally. The problem was that the hot water it produced was disappearing just as fast as it was being generated, draining away somewhere out of sight.

The Cause

During the call, the homeowner mentioned something they had not thought to raise earlier: they had occasionally heard the faint sound of water running somewhere behind one of the kitchen cupboards. They had assumed it was normal pipe noise and had not connected it to the heating problem.

That detail shifted our attention to the pipework serving an external shower on the opposite side of the kitchen wall, which was fed by the domestic hot water circuit.

The outdoor shower supply pipe had frozen during a period of cold weather and the resulting ice had split the pipe inside the wall cavity. Because the break was completely concealed within the wall structure, there was no visible damp patch, no water pooling on the floor, and no obvious sign that anything had ruptured.

Every time the heat pump heated the cylinder and pressure built slightly on the hot water side, water escaped through the split and drained away into the cavity. The cylinder would then cool rapidly, the heat pump would detect the drop in temperature and run another cycle, only for the same water loss to happen again. The system was unknowingly running in a continuous loop against a hidden leak. Our article on why a heat pump stops producing hot water covers the full range of causes for this symptom, including those that originate in the plumbing system rather than the heat pump itself.

The heat pump was entirely blameless. It had no way to distinguish between water that was being used intentionally and water that was escaping through a burst pipe, and it responded to both in the same way: by running another heating cycle.

The Temporary Solution

While the homeowner arranged for the permanent repair to be carried out, we guided them through isolating the hot water supply feed to the damaged section of pipework so the leak could not continue.

We walked through how to identify the relevant valve on the hot water circuit, explained what to check before closing it, and confirmed the isolation was complete once it was done.

With that section of pipework isolated, the change was immediate:

• The cylinder held temperature correctly for the first time in weeks, confirming beyond doubt that the leak had been the sole cause of the temperature drop

• Hot water availability returned to normal throughout the rest of the property

• The heating system stabilised and began performing as expected

• The homeowner retained the ability to manually restore access to the outdoor shower circuit when specifically required, while the rest of the system continued working normally

The Outcome

The heat pump had been operating correctly throughout the entire period of the problem. No fault was found with any component of the heat pump itself, no parts were replaced, and no specialist heat pump visit was required.

The actual cause was a burst pipe concealed within the wall cavity, caused by cold weather reaching an unprotected outdoor shower supply pipe that lacked any frost protection. Our guide on anti-freeze protection strategies for heat pump pipework is relevant reading for any homeowner with outdoor water supplies or exposed pipework connected to their heating system.

The homeowner arranged for the original installer to repair the split pipe and install proper frost protection on the outdoor shower supply to ensure the same situation cannot recur in future cold weather.

What This Shows

This case illustrates a pattern that appears regularly in heat pump diagnostics: a system producing symptoms that look like a heat pump failure when the actual cause lies entirely elsewhere in the building.

A structured diagnostic process, carried out remotely in under an hour, identified the precise cause without a site visit, without any parts being ordered, and without any work being done on the heat pump itself. The investigation used only what was directly observable: temperature readings, the behaviour of a valve, and the sound of running water. Our article on why heat pump repairs are often misunderstood in the UK discusses this pattern of misdiagnosis and why it is so common.

The heat pump in this case never had a fault. Had an engineer been dispatched without first understanding what the system was actually doing, a significant amount of time, money, and disruption could have been spent investigating a component that was never part of the problem.

Could This Have Been Avoided?

With some straightforward pre-emptive action by the original installer, yes. External pipework that passes through an uninsulated wall cavity and serves an outdoor fitting is vulnerable to frost damage if it is not provided with either adequate insulation, a drain-down capability, or a frost thermostat and trace heating. Including any of these at the time of installation would have prevented the pipe from freezing in the first place.

The cost of adding frost protection to an outdoor shower supply during the installation is minimal compared to the cost of locating and repairing a burst pipe inside a wall, or the disruption caused by weeks of reduced heating and hot water performance.

This case is also part of a broader pattern we encounter regularly: a heat pump that appears to have failed when the real problem is a separate component or an installation oversight elsewhere in the system. Similar situations include a case where three companies refused to investigate, assuming a heat pump fault, when the cause was simply a faulty zone valve and a case involving a faulty anti-freeze valve in a Suffolk property that was causing repeated pressure loss and heat pump lockouts. In both cases, as in this one, the heat pump unit itself was working correctly throughout.

If your heat pump is not producing reliable heating or hot water, is showing fault codes, or simply does not feel like it is behaving correctly, our Fix My Heat Pump service can identify what is actually happening before you spend money on unnecessary repairs.

Planning A Heat Pump Installation?

Some of the problems we diagnose remotely could have been prevented entirely at the design and installation stage.

Incorrect heat pump sizing, inadequately protected external pipework, unsuitable radiator specifications, and poorly configured zoning strategies can all create ongoing performance problems that trace back to decisions made before the heat pump was ever switched on.

Our Pre-Installation Design Review provides an independent assessment of the proposed heat pump design, giving homeowners confidence that the system is suitable before installation begins.

Identifying potential design weaknesses before installation is substantially easier and less expensive than tracing and correcting them after the system is in place.