Danfoss HIU Repairs & Services in London
Danfoss HIU Repair & Servicing
Danfoss is one of the UK’s most established HIU brands, known for reliability, durability and easy maintenance. With fewer electronic components and easily replaceable parts, many Danfoss HIUs are cost-effective to service and repair, with a potential lifespan of around 20 years when properly maintained.
Our SAV Systems-trained engineers have years of experience commissioning, servicing, repairing and installing Danfoss HIUs across London. Equipped with specialist tools, we provide a friendly, reliable and professional service.
Danfoss HIU servicing and repair visits cost starts from £120 + vat (£144), Monday to Friday, between 8am and 5pm.
Why Regular Danfoss HIU Servicing Matters
Regular Danfoss HIU servicing helps maintain efficiency, reduce energy waste and prevent costly breakdowns. Annual maintenance can identify faulty components, incorrect settings, leaks and corrosion early, helping extend your HIU’s lifespan and avoid unnecessary heating costs.
What’s Included in a Danfoss HIU Service?
Our Danfoss HIU servicing includes the following checks and maintenance:
- Heating Water Quality Test – Testing secondary heating water for inhibitor levels, corrosion indicators and pH.
- Strainer Filter Cleaning – Checking and removing blockages to maintain proper water flow.
- Leaks & Corrosion Inspection – Checking HIU components, valves and pipe connections for leaks, corrosion and visible defects.
- Heating Controls Inspection – Checking thermostats, actuators and heating controls.
- Heating Pump Checks – Inspecting pump operation and correcting settings where necessary.
- Primary Flow Rate Checks – Measuring primary heating flow rates and checking circulation.
- Heat Meter & Component Inspection – Reviewing individual heat meters and HIU components for visible faults.
- Digital Service Report – Emailed water test results, service records and digital service sheets after the visit.
- Repair Quotations – Fixed-price quotes for any additional repairs or replacement parts required.
- Annual Service Reminders – Automated reminders when your next HIU service is due.
Common Danfoss HIU Faults & Problems
Danfoss HIUs are reliable and easy to maintain, but certain components can develop faults over time. Below are some of the most common problems our engineers identify and repair.
1. Why is my Danfoss HIU producing no hot water or inconsistent temperatures?
No hot water, lukewarm water or changing temperatures can be caused by several faults within a Danfoss HIU. Possible causes include:
- Faulty Prepayment Valve – A noisy, seized or closed valve can stop the primary heating flow, leaving your property without hot water or heating.
- Blocked Strainer Filter – A clogged strainer can restrict primary heating flow, causing poor hot water performance, temperature drops or a complete loss of hot water.
- Faulty IHPT Hot Water Controller – A leaking, seized or incorrectly operating valve can cause lukewarm or excessively hot water.
- Blocked Plate Heat Exchanger – Scale or debris buildup can restrict heat transfer, resulting in poor hot water performance.
- Faulty AVTB Valve – A seized or incorrectly adjusted temperature control valve can affect hot water temperature.
The components fitted vary between models. An HIU engineer can inspect your unit and identify the cause.
2. Why are my radiators or underfloor heating not warming up with my Danfoss HIU?
If your radiators or underfloor heating are not warming up, the problem may involve circulation, heating valves or electrical controls. Possible causes include:
- Seized Heating Pump – A faulty circulation pump can prevent radiators or underfloor heating from warming up. Some pumps may display a red warning light when a fault occurs.
- Faulty TWA-V Actuators – Electrical faults or actuator failure can prevent heating valves from opening correctly.
- Faulty VMT Zone Valve – A leaking or stuck valve can restrict heating flow to radiators or underfloor heating.
- Faulty AVPL Valve – A seized or incorrectly adjusted differential pressure valve can affect heating performance.
- Power Supply or Thermostat Faults – A switched-off power supply or faulty room thermostat can prevent radiators or underfloor heating from operating.
- Underfloor Heating Controls – Faulty thermostats, wiring centres, actuators or manifold controls can prevent individual rooms or the entire underfloor heating system from warming up.
An engineer can check the HIU and connected heating controls to establish where the fault lies.
3. Why is my Danfoss HIU losing pressure or leaking water?
Repeated pressure loss or water around your Danfoss HIU can indicate a faulty component or leaking connection. Possible causes include:
- Faulty Pressure Gauge – Incorrect readings can make it difficult to identify low pressure or other heating system problems.
- Damaged Expansion Vessel – A failed expansion vessel can cause pressure fluctuations and repeated pressure loss.
- Leaking Safety Relief Valve – A faulty or discharging safety valve can cause the heating system to lose pressure.
- Leaking IHPT Valves and Pipe Connections – Worn or damaged seals at valve joints and pipe connections can cause water leaks within the HIU.
Leaks and repeated pressure loss should be investigated promptly to identify the cause and reduce the risk of damage.
Danfoss HIU Fault Diagnosis & Repairs
Whether you contact us about no hot water, heating problems, water leaks or routine annual servicing, our engineers will inspect your Danfoss HIU and identify any faults. Where possible, repairs are carried out during the visit, or temporary measures are taken to restore heating and hot water until replacement parts are available.
Replacement Parts & Warranty
If any Danfoss HIU components need replacing, we provide a fixed-price quote before carrying out the work. We source replacement parts from reputable suppliers, with all parts and labour covered by a 12-month warranty.
If several HIUs need a service, we can offer a discount package for a group of service bookings in London.
For more information about how our team could help you with your Danfoss services in London, please do not hesitate to contact us via our contact form or by calling 02088224451. Learn more about HIU – Click here.
Looking to improve your heating and hot water system? Click the link to see our top recommended products.
Danfoss HIU FAQs
How often should a Danfoss HIU be serviced?
A Danfoss HIU should usually be serviced once a year. Annual servicing helps keep the unit clean, checks that its controls are working and can identify worn parts before they cause a breakdown.
Regular servicing may also improve heating and hot water performance. Add Detail provides digital service records and can send an annual reminder when the next service is due.
What are the signs that my Danfoss HIU needs a repair?
Common warning signs include no heating, poor hot water, changing water temperatures, unusual noises, low pressure or leaks around the unit.
You may also notice that radiators take longer to warm up or that the hot water becomes cold after a few minutes. These problems can be caused by blocked filters, a faulty control valve, a seized pump or a restricted heat exchanger.
Which Danfoss models can you service?
Our engineers work with Danfoss HIUs, including units sold under the Gemina, Termix and Redan ranges. We also service and repair HIUs from a wide range of other manufacturers.
The exact layout and parts can vary between models. Providing a photograph of the HIU and its model label when booking can help our team identify the unit and prepare for the visit.
Why is my Danfoss HIU not producing hot water?
A lack of hot water can have several causes. The building’s central heat supply may be unavailable, or the HIU may have a blocked filter, incorrect temperature setting or restricted plate heat exchanger.
Faulty thermostatic controllers and circulation problems can also affect performance. An HIU engineer can test the unit and check whether the fault is inside the apartment or elsewhere in the communal heating system.
Can you repair a leaking Danfoss HIU?
Yes. Most leaks can be repaired by replacing the faulty seal, valve, pipe or other affected part. The source of the leak must first be found, as water can travel along pipes and appear away from the actual fault.
Leaks should be checked quickly. Even a small leak can damage electrical parts, cupboards, flooring or the property below.
Should I repair or replace my Danfoss HIU?
Repair is often the best choice when the HIU is in good condition and the required parts are still available. Replacing a pump, valve, sensor or heat exchanger may restore normal performance without replacing the full unit.
A new HIU may be more suitable when the existing model is old, breaks down often or needs several costly repairs. An inspection can help determine which option offers better long-term value.
Can you service several HIUs in the same building?
Yes. We offer group servicing for blocks and developments with several HIUs. A discounted package may be available when multiple residents, landlords or a managing agent arrange visits together.
Group bookings can make access easier to organise and help ensure that units across the building receive regular maintenance.
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