OFTEC Heat Pump common mistakes
OFTEC Heat Pump · Understand the traps and how to avoid them.
Sizing the heat pump from the existing boiler's rated output or from a rule-of-thumb kW-per-m² figure instead of a room-by-room heat loss calculation.
The boiler output is convenient and visible, and candidates assume like-for-like replacement; they skip fabric survey and U-value work under time pressure.
What to do instead
Always start from a full room-by-room heat loss calculation using measured room dimensions, construction, glazing and design external temperature; treat the existing boiler rating as irrelevant to sizing.
Selecting a heat pump without checking that its output at the design external temperature (with defrost allowance) covers the calculated heat loss, relying only on the nominal A7/W35 rating.
Manufacturers headline the mild-weather rating, and candidates compare that number directly with the heat loss figure.
What to do instead
Compare the calculated design heat loss against the unit's declared capacity at the design external temperature and flow temperature, applying the manufacturer's defrost and back-up allowances.
Designing the distribution system at flow temperatures and ΔT that the existing radiators cannot deliver, without resizing emitters or checking output at the lower flow temperature.
Candidates carry over a 70/50 or 80/60 mindset and assume existing radiators are adequate; they do not recalculate emitter output at the heat pump's lower flow temperature.
What to do instead
Calculate each emitter's output at the proposed flow/return temperatures and design ΔT, and upsize or add emitters where output falls short; document the resulting design flow temperature.
Commissioning without completing and recording the full commissioning checklist, including measured flow rate, ΔT, refrigerant charge verification and heat pump performance checks.
Time pressure on site and treating commissioning as a formality; candidates rely on the unit running rather than on measured evidence.
What to do instead
Work through the manufacturer's commissioning procedure item by item, record measured values (flow rate, temperatures, pressures, electrical readings) and retain the signed schedule as part of the handover pack.
Failing to balance the system or set the correct primary/secondary flow rates and buffer arrangement, leaving the heat pump short-cycling or unable to reach design ΔT.
Candidates assume the heat pump's internal pump and factory settings will suffice, and do not treat hydraulic balancing as a commissioning step.
What to do instead
Balance all circuits to design flow, confirm the required minimum system volume or buffer is present, verify the design ΔT at steady state, and adjust pump speed/settings accordingly before sign-off.
Not evacuating the refrigerant circuit properly (or skipping pressure/leak testing) before charging on split systems.
Candidates rush the vacuum stage or trust that factory-charged lines are clean; they underestimate the effect of moisture and non-condensables.
What to do instead
Pressure-test with OFN, evacuate to the manufacturer's specified micron level and hold the vacuum test for the stated duration, then charge by weight per the data plate and record the results.
Specifying or wiring the heat pump supply without correct protective device ratings, cable sizing and dedicated circuit arrangements, or omitting the required isolation and lock-off provisions.
Candidates apply domestic socket-circuit habits to a fixed high-current appliance and overlook inrush, diversity and the manufacturer's supply requirements.
What to do instead
Size cables and protective devices from the manufacturer's electrical data (including starting current and any soft-start), provide a dedicated circuit with appropriate isolation, and verify earthing and bonding before energising.
Misconfiguring controls - weather compensation curve, set-back, DHW priority and cylinder/immersion control - so the system runs inefficiently or fails to deliver hot water.
Candidates leave factory defaults or copy boiler-style settings, and do not verify the control strategy against the design intent.
What to do instead
Set the weather compensation curve to the design flow temperature at design external temperature, configure DHW priority and legionella cycle, and demonstrate and record each setting at handover.
Carrying out service and maintenance without following the manufacturer's schedule, and failing to record refrigerant checks, electrical tests and performance readings.
Candidates treat servicing as a visual glance and a filter clean, and do not produce auditable records.
What to do instead
Use the manufacturer's service schedule as a checklist, include refrigerant leak/charge checks and electrical safety tests, and complete a written service record with measured values for the customer and file.
Overlooking regulatory and notification obligations - building regulations notification/competent person route, F-Gas obligations for refrigerant handling, and correct handover documentation.
Candidates focus on the technical install and assume paperwork is someone else's responsibility, or are unsure which regime applies.
What to do instead
Before work, confirm which notification route applies, ensure refrigerant work is done by appropriately certified personnel with F-Gas records, and issue the full handover pack including commissioning records, instructions and warranties.