EK on an IVT Greenline HT Plus: Electric cassette (EK) alarm: the electric additional heater miniature circuit-breaker or overheat protection has tripped
Short answer
On an IVT heat pump, EK means: Electric cassette (EK) alarm: the electric additional heater miniature circuit-breaker or overheat protection has tripped. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Electric cassette (EK) alarm: the electric additional heater miniature circuit-breaker or overheat protection has tripped.
Part involved: electric cassette MCB (fuse 3) / overheat protection (fuse 4).
Likely causes:
- Electric cassette MCB tripped; electric cassette overheat protection tripped - most frequently due to poor flow over the cassette (air in heat pump or clogged particle filter).
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Manual reset: Ackn. button on Rego 637 control panel.
What you can check
- Press the Ackn. button on the control panel once (the manual says there is no risk in resetting an alarm; the heat pump restarts within 15 minutes if heat is needed). If the alarm returns, contact your installer. Check the heating-system pressure gauge is in the range given in the user guide (Thermia/Danfoss: 1-1.5 bar when cold) - do not top up yourself unless you have been shown how; check radiator/underfloor valves and room thermostats are open.
What the engineer will check
- Reset cassette MCB (circuit breaker 3) and overheat protector (button 4, press firmly); clean hot-side particle filter; vent; investigate repeated trips.
Who to ask for: heat pump engineer.
Certification: Qualified electrician / heat pump engineer (electrical fault-finding).
What you might notice
Sources
- Greenline HT Plus C and E Guide to installation, commissioning and maintenance (Art. no 290410-29, v1.1) ↗ · 290410-29 v1.1 · page p.36 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026