Replacing an Old Heat Tracing System
Many plants have heat tracing installed 15–25 years ago: constant wattage cable, mechanical thermostats, no monitoring. It worked once. Now circuits trip, thermostats are stuck, and spares are obsolete. This guide covers when to repair, when to replace, and how to replace it without repeating the old mistakes.
Signs the old system is at end of life
- Repeated earth faults or tripping RCDs after rain
- Insulation resistance falling year on year at the same circuits
- Mechanical thermostats with a wide deadband, or stuck closed
- Obsolete cable or accessory types that are hard to source
- No circuit monitoring, so failures are found by freeze events
- Insulation and cladding degraded beyond repair on the same lines
Repair or replace?
| Situation | Typical action |
|---|---|
| One or two faulty circuits, rest healthy | Repair terminals or replace sections |
| Multiple circuits failing on the same lines | Replace the tracing on those lines |
| Insulation and cladding at end of life | Replace tracing together with insulation |
| No monitoring, failures recurring | Upgrade controls to monitored circuits |
| Cable type obsolete | Replace with current equivalent; update drawings |
What to change when replacing
1. Cable selection
Constant wattage was often chosen for fixed output. Today self-regulating cable is usually the better fit for freeze protection because it can be cut on site and limits overheating — but check the output at the design ambient before switching types.
2. Controls
Replace mechanical thermostats with electronic controllers and add circuit monitoring or alarms. This is the single biggest reliability improvement in most retrofits.
3. Protection
Check breaker and RCD ratings against the new cable and the actual circuit length; do not reuse protection sized for the old system without checking.
4. Documentation
New as-built drawings, circuit schedule and test records. Old drawings are usually wrong after 20 years of modifications.
Planning the replacement
- Survey each circuit: cable type, length, insulation condition.
- Decide per line: repair, replace tracing only, or replace tracing with insulation.
- Schedule in the maintenance window before winter, not during it.
- Keep the old circuit numbers where possible to limit drawing changes.
- Plan for waste: old cable and insulation removal.
Testing after replacement
Insulation resistance, continuity, earth continuity, operating current and functional tests per circuit, plus alarm tests. Compare with the design values and record everything for the next 20 years.
Common retrofit mistakes
- Replacing cable but keeping failing mechanical thermostats.
- Reusing protection without checking the new load.
- Mixing cable types on one circuit.
- Not updating drawings and circuit schedules.
- Doing the work in winter, when access and conditions are worst.
System replacement?
Send the existing circuit list and a few photos. We assess repair versus replacement and propose the new design.
Request an Assessment