We will be sharing real-world insights into common issues that lead to buried heat network failures, based on more than 13 years of hands-on experience investigating, repairing and delivering underground heat infrastructure.
While not everyone may agree with every detail we share, our goal is simple: to support those delivering new or expanded networks with practical, experience-based guidance that helps avoid costly mistakes.
One of the failure points we see is poor / incomplete designs and specifications or disregard for them during installation. Buried pre-insulated heat networks present specific technical challenges quite different from other underground services. That’s why robust standards like CP1 and EN13941 exist and why they matter.
While many consultants in the UK market deliver high-quality, detailed specifications and actively govern their implementation, we also regularly encounter:
The result? Lowest-cost suppliers win work by cutting corners and the long-term integrity of the network is compromised.
PPSL District Heating is currently remediating several networks that we (and other reputable contractors) previously tendered for, all awarded to contractors who failed to meet specification or industry standards.
We strongly recommend engaging a consultant with a proven track record in buried heat networks capable of producing:
1. Inadequate Expansion & Contraction Design
Failures due to incorrect tees utilised, uninstalled foam pads, or burial depth that does not match the design.
Expansion design must account for:
2. Use of Inappropriate Below-Ground Components
Valves, H-bypasses, and exposed steel not designed for underground use often corrode prematurely. Only use components built for buried systems. We see these regularly make their way into buried networks resulting in early failure. We also see conventional loops utilised for long term use on below ground branches, which eventually corrode. Specifications typically just state “loops” with no further detail, leaving it open to interpretation.
3. Components Not Rated for the networks Pressure/Temperatures
Gaskets, valves, or tees that don’t meet system requirements. Additionally, not all pre-insulated components are 25 bar rated. Check every product by ensuring they are all in a tech spec preconstruction and thoroughly reviewed. Check actual products installed are what was quoted / included in the specification.
4. Outer Casing Joint Failures
Joint selection often doesn’t match ground conditions or specification. Quality and compatibility can vary so you must make sure the joints utilised are what was in the specification and you understand the difference. We see specifications that state fusion welded joints then see that the client has used shrink joints for the example.
5. Flanged Joints Below Ground
Flanges can corrode and fail, especially under stress from expansion and when utilised in below ground chambers exposed to the elements. Avoid their use in buried systems or chambers wherever possible.
6. Dead Legs and Future Connection Points
Weld capped ends / branches left exposed below ground will corrode. We have seen this happen in just two years. If left with no loop and bypass with none circulating water they can also become a breeding ground for bacteria. Instead:
7. Damage from Other Trades/Structures
Poor route coordination can lead to services clashing or damaging pre-insulated pipes as other contractors re-excavate in close proximity. You must ensure that you have:
8. Poorly Designed / Specified Valve Chambers
Incorrect chamber designs / sizing can cause spindles to bind during expansion and contraction, restricts access for maintenance, or creates standing water. Chambers must:
The introduction of HNTAS (Heat Network Technical Assurance Scheme) is a positive step towards enforcing quality and governance throughout a project’s lifecycle. But until it’s universally adopted, diligence in design and oversight remains essential.
If you’re involved in the design, delivery, or management of heat networks we hope these insights help you avoid costly pitfalls. We will be covering more topics in the coming weeks.
Need help diagnosing or reviewing a buried network? Please get in touch with PPSL District Heating. We’d be happy to help.
