The Boiler Graveyard to Heat Pump Haven in the West Midlands

Helping YOU find good heating engineers. We share case studies from engineers in the Guild of Master Heat Engineers to help people find top installers, help gas and oil engineers increase their knowledge around heat pumps, and provide a solution for third-sector professionals to understand the industry better.

Overview

A brand-new, modern home should be a bastion of warmth and comfort. But for Neil's customers, whose 304 sqm, four-bedroom property in the West Midlands was built in 2016, that was far from the reality. Despite having ground and first-floor underfloor heating, the house was notoriously cold, and its heating system was caught in a cycle of catastrophic failure. It is believed the property has gone through five separate gas boiler replacements, all failing due to leaking heat exchangers and all conducted under warranty.

This case study demonstrates how quality engineering, rooted in a deep understanding of system water quality and component protection, solved a catastrophic failure cycle that five replacement heating appliances and conventional maintenance practices could not.

Master Heat Engineer

Key Specifications

• Property Type: Modern, 304 sqm, 4-bed house with UFH (Built 2016)

• Design Heat Loss: Estimated 12.35kW @ -5.13°C

• Heat Pump Installed: Viessmann 150-A 16kW

• System Configuration: Open Loop

• System Preparation: Thoroughflush clean

• Monitoring Validation: OEM (Open Energy Monitor)

The Challenge: Chronic Water Quality and System Oversizing

When the Master Engineer investigated in March 2024, the evidence pointed overwhelmingly to a devastating combination of chronic water quality neglect and system oversizing. The boiler industry has often relied on simply dumping inhibitors into a system and believing the problem is solved; however, this approach failed entirely here.

The team noticed sand-like debris while draining the system. This residue was collected and sent for analysis by the customers’ son, who works at a university, and confirmed the presence of aluminium (likely from the heat exchangers).

Furthermore, the existing boiler was significantly oversized, leading to constant on/off cycling (short cycling). This mechanical and thermal stress, combined with the circulating corrosive residue from past failures, created the precise conditions for persistent heat exchanger failure in every new boiler. The customers had never been warm all winter, the running costs were high, and the system was suffering from catastrophic internal component degradation.

System Design

The required solution involved meticulous planning, proper sizing, and a comprehensive system preparation and setup to protect the new heat pump installation:

A heat loss calculation was performed, confirming an estimated total heat loss of 12.35kW at the design temperature of -5.13°C. This gave the installation team the exact target output needed.

The team installed a Viessmann 150-A 16kW heat pump, which delivered an optimal output of 12.68kW at design conditions, perfectly matching the required load. This was paired with a high-performance cylinder.

The system was subject to a meticulous Thoroughflush clean, a brand highly rated by Master Heat Engineers, designed to remove all system contamination and ensure optimal conditions for the new heat pump.

The existing cylinder was poorly located in the centre of the house. It was moved to the utility room, allowing the team to cleverly repurpose the old primary pipework for the underfloor heating manifolds, streamlining the installation.

Finally, all existing pump sets and actuators were removed, and the system was configured for open loop control. This approach allows the heat pump to precisely manage flow and temperature, ensuring good efficiency and comfort delivery to the underfloor heating, and eliminating the damaging short-cycling issue.

Performance and Results

The quality of the installation and its subsequent performance were immediately validated: the system's performance data was confirmed by the OEM (Open Energy Monitor), a brilliant open-source monitoring platform (run by Glyn and Trystan), proving the successful install.

The real proof came from the customers’ own monitoring after a full year of operation, showing dramatic improvements:

• Annual Heating & Hot Water Cost: Reduced from circa £1,800 (Gas) to under £800 (Heat Pump), resulting in over £1,000 saving.

• Home Comfort: The house transformed from being cold all winter to being warm all winter, marking the first comfortable year since 2016.

The dramatic reduction in running costs was significant, but the impact on the customers’ quality of life was profound.

Key Takeaway: Correct heat loss calculation combined with full system diagnosis and decontamination is crucial for heat pump success.

Estimated Heat Loss (kW) at Various Outside Temperatures

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Podcast

Take a listen to a podcast I did recently discussing how radiators are being sold in the UK which are not able to meet their claimed heat output. My guests for this episode were two of the Guild Patrons: Castrads and UK Radiators who have been helping resolve this issue. As well as listening you can also watch us here

Closing Thoughts

This case study, where a new build’s boiler seems to have been replaced five times before installing a heat pump (and congratulations to the customer for getting their heat pump), starkly highlights (I believe) three major flaws in the traditional heating sector.

1. Water Quality, VDI 2035, and Market Chaos

It’s astonishing that water quality issues and corrosion still plague us. Chemical inhibitors first came to the merchant shelves the year I was born (71) yet we still struggle. Why? One reason is the UK inhibitor industry has failed to promote the fact that high water temperature accelerates the rate of corrosion.

Crucially, the case study noted the importance of good quality flushing procedures with thoroughfush equipment being used and VDI 2035 methods. This standard addresses the modern challenge of systems containing a vast number of materials (not just metal like in the old days when chemicals came to market) and benefits from a scientific, systematic approach to treatment.

However, the reality is chaotic: the market is oversaturated with many, many brands of inhibitors. This means engineers often buy whatever is available or cheapest, leading to no one truly knowing what's in a system. Inhibitors require a methodical, scientific application, which this hyper-competitive market prohibits. Tellingly, associations linked to the UK's largest inhibitor players seem resistant to even the mention of robust standards like VDI 2035

2. The Flawed Control Strategy: On/Off Cycling

This water quality issue links directly to the second problem: on/off control, especially with oversized boilers. This method is fundamentally flawed - it’s high-temperature heating by another name. The resulting short cycling causes issues for expansion vessels as well as thermal stress and damage to low water content heat exchangers, a downside long detailed by research (e.g., in fracture mechanics). Despite decades of study, UK industry control associations, like BEAMA’s, have seemed to dismiss the true severity of cycling.

3. Selling Stuff Over Solving Problems

Thankfully, the UK heating sector is now under intense scrutiny. It's becoming easier for outsiders to see that science often contradicts the industry's historical path. Without a doubt, the saturated competition and pressure to sell stuff has led to engineering common sense being lost along the way.

It's time for manufacturers (especially their marketing departments) and long established associations to pay close, joyous attention to the science. Many heating engineers are finally having this reawakening.

The ultimate failure illustrated here is that the industry has been content to constantly replace stuff (selling) rather than committing to addressing the root cause of frequent breakdowns (engineering). The case study isn’t just about a broken boiler; it’s about a broken philosophy.

In fact, the case study is about a happy customer and an engineer committed to learning as much as possible in this exciting sector. I had the pleasure of meeting Neil recently with a few other engineers for dinner. He remarked how he got into heat pumps from listening to my podcast. It’s great for me to see how all these strange communication platforms we all now live with (in my case a podcast) can inspire people to learn.

P.S. This case study is also about a new build. With a boiler system which kept failing. How can that really be happening in this day and age. Heat pump manufactures are all looking to get into the new build sector. Lot’s of selling tactics will ensue and all ready underway (trust me). We need to be careful common engineering sense is not forgotten.

Nathan

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