HIU Repair London & M25

HIU repair, servicing and maintenance

A heat interface unit takes heat from a communal or district network and transfers it to a single dwelling for heating and instantaneous hot water. Because everything passes through one compact unit, a single failed component takes out both services in the flat. We repair rather than replace where the body and heat exchangers are sound, carry common valves, actuators, sensors and seals, and service units on a planned cycle so faults are caught before residents report them. HIU servicing covers strainer cleaning, heat exchanger performance checks, control calibration, valve travel and a full temperature and flow record.

• HIU repair and emergency fault attendance
• HIU service and annual maintenance visits
• Strainer and filter cleaning on primary and secondary sides
• Temperature, flow and return performance recorded
• Planned maintenance contracts for blocks and estates

Fault finding and diagnostics

Most HIU complaints reduce to a short list of causes, and getting the diagnosis right on the first visit avoids repeat call-outs. Heating working but no hot water usually points at the domestic hot water plate heat exchanger, its control valve or the flow sensor. Hot water but no heating is generally the heating control valve, actuator or a zone/thermostat fault in the flat. Nothing at all is often a loss of primary flow across the whole riser rather than a fault in the unit itself. Poor hot water flow or lukewarm water is commonly a scaled or blocked exchanger, a partially blocked strainer, or a low differential pressure across the unit.

• HIU fault finding and diagnostics in flats and plant rooms
• HIU not working, no hot water or no heating
• Heating but no hot water, and hot water but no heating
• Low hot water pressure and poor flow rate
• Temperature too hot, too cold or fluctuating
• Primary differential pressure and keep-warm checks

Leaks and leaking heat interface units

A leaking HIU is urgent because the primary side runs at high temperature and the unit usually sits in a cupboard above a finished floor. Leaks typically come from compression joints disturbed at installation, a failed gasket on a plate heat exchanger, corroded isolation valves, or the pressure relief discharging because an expansion vessel has lost its charge. We isolate the unit, trace the source rather than guessing, replace the failed joint, valve or exchanger, refill and pressure-test, then check the ceiling below for damage that needs reporting to the managing agent.

• Leaking heat interface unit isolated and made safe
• Failed gaskets, seals and compression joints replaced
• Corroded isolation and check valves changed
• Relief valve discharge and expansion vessel faults

Component repairs and replacements

Repairing components in situ keeps costs down and avoids the disruption of changing an entire unit. We replace HIU control valves and actuators, differential pressure control valves, temperature sensors and thermostats, circulating pumps in pumped units, and both the domestic hot water and heating plate heat exchangers. Where an exchanger is scaled rather than failed we clean or chemically flush it and re-test the hot water flow rate against the original design figures. Blocked exchangers are a common cause of gradually worsening hot water in hard-water areas across London.

• HIU valve replacement and control valve repair
• Actuator replacement and recalibration
• Plate heat exchanger replacement and heat exchanger cleaning
• Blocked HIU heat exchanger descaled and flushed
• Strainer cleaning and filter replacement
• HIU pump replacement and thermostat repair

Communal and district heating

We work across communal heating systems and district heating networks, from single blocks with a central boiler plant to estate-wide schemes fed by an energy centre. That means we look beyond the individual unit: poor performance in one flat is a unit fault, but poor performance across a riser is usually a network problem — insufficient differential pressure, high return temperatures, a failing pump or unbalanced circuits. Our communal heating engineers cover London boroughs and M25 towns and report findings in a form that managing agents, RMCs and housing providers can act on.

• Communal heating HIU repair for blocks and estates
• District heating HIU repair and network checks
• Riser and plant room investigation where several flats are affected
• Reports for managing agents, RMCs and housing associations

Emergency and same-day HIU repair

No heating or hot water in a home is an emergency, particularly for older residents and families. We hold same-day slots across London and operate a 24 hour HIU engineer callout for blocks under contract. Call 0208 935 5572 and we will confirm an arrival window, attend with common HIU spares on the van, and where a part has to be ordered we will leave the property with heating or hot water available wherever it is technically possible.

Areas we cover for HIU repair

Our HIU engineers cover the whole of London and the M25, including Camden, Islington, Hackney, Tower Hamlets, Southwark, Lambeth, Wandsworth, Westminster, Kensington & Chelsea, Greenwich, Lewisham, Newham, Barnet, Brent, Ealing and Croydon, plus M25 towns such as Watford, St Albans, Enfield, Romford, Dartford, Bromley, Kingston, Staines, Slough, Woking and Epsom. Most new-build and regeneration schemes in these areas run on communal heating, so we are usually already working nearby.