What Is an HIU and Why Does It Need Servicing?
If you live in a flat or apartment connected to a communal or district heating network, chances are your home relies on a Heat Interface Unit — commonly known as an HIU. This wall-mounted unit is the equivalent of your individual boiler. It takes hot water from a shared heat network and converts it into heating and domestic hot water for your property alone.
Unlike a traditional boiler that burns gas on-site, an HIU transfers heat through a plate heat exchanger. It's a cleaner, more efficient system when maintained properly — but like any mechanical equipment, it degrades without regular servicing. We provide specialist HIU service in London for residents, landlords, and block managers across every borough within the M25.
Why Annual HIU Servicing Matters
An unserviced HIU doesn't just run less efficiently — it can fail entirely, leaving you without heating or hot water. Here's what happens when maintenance is neglected:
- Scale buildup on the plate heat exchanger — London's hard water causes calcium deposits that reduce heat transfer by up to 30%. Your heating takes longer to warm rooms and your hot water temperature drops.
- Valve seizure — Control valves that aren't exercised regularly can seize in position, preventing the unit from regulating flow correctly.
- Strainer blockage — Debris from the communal network collects in the HIU's strainer, restricting flow and causing pressure drops.
- Sensor drift — Temperature sensors lose accuracy over time, causing the unit to over- or under-heat your water.
- Expansion vessel failure — The internal expansion vessel loses its charge, leading to pressure fluctuations and potential leaks.
Annual servicing catches all of these issues before they become expensive repairs. At £195 for a fixed-price HIU service, it's a fraction of the cost of an emergency callout or unit replacement.
What Does a Professional HIU Service Include?
A thorough HIU service from a qualified heating engineer should take approximately 60–90 minutes and cover the following:
Inspection and Diagnostics
- Visual inspection of the entire unit for leaks, corrosion, or damage
- Check all pipe connections, isolation valves, and fittings
- Inspect the plate heat exchanger for signs of scaling or fouling
- Test primary and secondary pressures
- Check the expansion vessel pre-charge pressure
Cleaning and Maintenance
- Clean or replace the strainer/filter
- Descale the plate heat exchanger (if required)
- Exercise all motorised valves to prevent seizure
- Check and clean temperature sensors
- Inspect and test the pressure relief valve
Performance Testing
- Measure flow rates on both primary and secondary circuits
- Test domestic hot water delivery temperature (target: 50–55°C at the tap)
- Check heating circuit delta-T (the difference between flow and return temperatures)
- Verify the unit responds correctly to demand signals
- Test the time taken to reach full hot water temperature
Documentation
- Record all readings and measurements
- Issue a service certificate with engineer details
- Flag any developing issues with recommendations
- Provide records suitable for Ofgem compliance audits
HIU Brands We Service Across London
Our engineers are manufacturer-trained on all major HIU brands installed across London's district heating networks:
- Danfoss — The most common HIU in London new-builds. We service all Danfoss Redan models including the Akva Lux II and the newer VX range.
- Alfa Laval — Found in many large developments across Nine Elms, Greenwich, and Canary Wharf.
- SAV Systems — We hold SAV approved contractor status, meaning we're certified to work on their full product range.
- Evinox — Common in London residential schemes, particularly their ModuSat range.
- Heatrae Sadia — Their Megaflo HIU range is found in several Battersea and Wandsworth developments.
- Caleffi — Increasingly popular in new London builds for their compact design.
If your unit isn't listed here, call us on 020 7622 0444 — we've yet to encounter an HIU brand we can't service.
Ofgem 2027 Compliance: What Block Managers Need to Know
From January 2027, Ofgem's new Heat Network regulations require all registered heat networks to demonstrate compliance with technical standards — including proof of regular HIU maintenance across the network. This isn't optional. Non-compliant networks face enforcement action and potential fines.
For block managers and managing agents, this means:
- Documented annual servicing of every HIU on the network, with full service records
- Performance data showing units operate within manufacturer specifications
- Remediation evidence where underperforming units have been repaired or replaced
- Qualified contractor records — engineers must hold appropriate qualifications
We provide Ofgem-ready service documentation as standard, with digital records, audit trails, and compliance reports that satisfy regulatory requirements. For blocks with 10+ units, we offer planned maintenance contracts with scheduled visits, bulk pricing, and a dedicated account manager.
Who Needs HIU Servicing?
Residents
If your flat is connected to communal heating, your HIU is your responsibility (unless your lease states otherwise). Annual servicing keeps your heating reliable and your hot water consistent. Most importantly, it prevents the unit failing in winter when you need it most.
Landlords
Your tenants expect reliable heating and hot water. An HIU failure means an unhappy tenant and an emergency callout — both avoidable with annual servicing. Our care plans cover annual HIU servicing with priority response if anything goes wrong between visits.
Block Managers and RMCs
Managing a block with 20, 50, or 200+ HIUs requires a systematic approach. We offer block-wide planned maintenance contracts with:
- Scheduled service visits coordinated with residents
- Bulk pricing from £165 per unit for blocks of 20+
- Digital service records for every unit
- Priority emergency response for the block
- Quarterly performance reports
- Ofgem 2027 compliance documentation
Get in touch for a bespoke maintenance proposal for your development.
How Much Does an HIU Service Cost in London?
Our fixed pricing for HIU servicing in London:
- Individual HIU service: £195 (fixed price, no hidden extras)
- HIU service + descale: From £295 (where significant scaling is found)
- Block contracts (20+ units): From £165 per unit
- Emergency HIU attendance: £150/hour (1-hour minimum, Mon–Fri)
There's no call-out fee, no congestion charge surcharge, and no hidden costs. The price we quote is the price you pay.
Why Choose Heat-Plex for HIU Servicing in London?
We're not a general plumber who occasionally looks at an HIU. District heating is a core specialism for our team:
- SAV approved contractor and manufacturer-trained on Danfoss, Alfa Laval, Evinox, and all major brands
- In-house employed engineers — no subcontractors, ensuring consistent quality and accountability
- Battersea HQ (SW8) — we're based in the heart of London's largest concentration of district heating developments
- Same-day availability for urgent HIU repairs across London
- Audit-grade documentation ready for Ofgem 2027 compliance
- 45,000+ jobs completed since 2015, with a 4.9-star rating from 286 reviews
Book Your HIU Service Today
Whether you're a resident needing your annual service, a landlord protecting your investment, or a block manager planning maintenance across an entire development — we're ready to help. Our specialist HIU engineers cover all London boroughs within the M25, with same-day attendance available for urgent issues.
Request a quote online or call us on 020 7622 0444. For block maintenance contracts, email contact@heatplex.com with your development details and unit count.