Desludging of the networks

Sludge removal from heating/chilled water/domestic hot water aims to remove sludge, oxides, scale, and biofilms accumulated in pipes, heat exchangers, underfloor heating systems, fan coil units, and boilers/heat pumps. These deposits reduce pipe diameters, block valves, degrade the temperature difference (ΔT), increase pumping consumption, and decrease efficiency (warm emitters, excessively hot returns, more frequent defrosting). Properly conducted sludge removal restores flow rates, reduces noise, and stabilizes system controls.

Sludge removal: operational definition and methods

We begin with a diagnosis: sampling (total iron, magnetite), inspection of sludge traps and filters, ΔT/ΔP readings, and identification of cold spots in floors. Depending on the network and materials:

- “High speed” hydraulics : rinsing by flushing in successive loops, until clear water (pay attention to the permissible pressure).

- Chemical : dispersant/deoxidizer/descalant dosed and circulated for a few hours/days, then neutralized and rinsed. "Gentle" version for underfloor heating systems using PER/MLC.

- Power-flushing (dynamic) : mobile unit with high pulsed flow rate + filtration.

- Capture & protection : cyclonic/magnetic sludge remover on boiler/heat pump return, sludge trap on loop, microbubble degasser, continuous side-stream filtration.

- Preventive treatment : corrosion inhibitor, pH/hardness control, air purging, adapted pump speed (avoid erosion).

- Deliverables : report (photos, before/after measurements, conductivity, turbidity), restored ΔT curve, maintenance plan (purges/filters).

Advantages, limitations and points to consider in sludge removal

Interests

• ΔT and restored flow rates → boiler/heat pump efficiency increases.
• Comfort: uniform emitters, reduced noise and whistling.
• OPEX ↓: reduced pumping, less frequent defrosting/machine cycles.
• Durability: valves/heat exchangers are preserved, fewer breakdowns.

Boundaries

• May reveal latent leaks (worn seals).
• Chemical compatibility to be checked (aluminium, joints, floors).
• Waste and effluent management (neutralization/traceability) to be planned.

Points to consider

• Zone-based sequencing to avoid clogging elsewhere; bypass of sensitive equipment.
• Measurements before (iron, turbidity, ΔT/ΔP) and then after to prove the gain.
• Certified reagent choices, respect for contact times and neutralization.
• Install magnetic sludge remover + degasser and periodic purging plan.
• Water quality monitored (pH, TH, conductivity) + inhibitor maintained.
• GTB coordination (pump speeds, temperatures) during operation.

Anecdote — “Underfloor heating that came back to life in Metz”

In Metz, an office building with underfloor heating had warm areas and pumps running at full capacity. Samples showed high magnetite levels. The team carried out a gentle, looped chemical descaling process, installed a magnetic sludge separator on the boiler return line, and a deaerator. After flushing/neutralization and the addition of an inhibitor, the temperature difference normalized, the valves stopped seizing, and the pumping power dropped by 28%. The building manager laughed: "We weren't heating the concrete anymore... we were finally heating the offices."