Common problems
Symptom-first troubleshooting for the UNI 60 — blank controller screen, fan humming but not turning, STB overheating, poor draft, failed fire-up and low output.
Start with the symptom, not the component. Every entry here links to the page with the full procedure.
The fan does not turn, or turns very slowly
If your fan makes a humming sound and does not turn, the minimum fan speed is too low.
Go to boiler settings and set the minimum fan speed to 40 %.
Set the maximum fan speed to 80 %.
Confirm fan type = WPA 07 / DM85. The wrong fan type creates a dead band where parameter changes produce no visible effect.
Blank screen
Verify the connection using the electrical diagram, and make sure the controller is switched ON. Then verify these parameters with a multimeter:
220 V on L and N.
Controller fuse continuity. 250 V, 3.15 A, 5 × 20 mm.
Continuity at terminal I1. If there is none, jump this contact to test — an open STB circuit will hold the controller down.
If none of this works, disconnect everything from the controller except L, N and the jumpers, then retest.
Also check the TR2_DISP panel ribbon, especially after a controller swap.
STB overheating
The external safety thermostat has tripped — the water reached roughly 90 °C.
To clear the alarm the boiler temperature must fall below 60 °C, and the alarm must be reset manually on the control panel. Per PN-EN 303-5:2012 the fan cannot restart on its own.
| Likely cause | Check |
|---|---|
| Pump not running | Q3 output, pump power, 220 VAC relay for 120 V circulators |
| All zones closed, no bypass | Fit a flow bypass |
| Pump start temperature too high | MBtek value 35 °C / 95 °F |
| Boiler cooling temperature too high | MBtek value 78 °C / 172 °F |
| Air lock | Vent the system |
| Power outage mid-burn | Expected — reload after power returns |
If you need to operate at a higher temperature, order a DZT-2 (opens 200 °F / 95 °C) and connect to I1.
→ Alarms
Smoke comes into the room
| Cause | Fix |
|---|---|
| Poor draft | Check with a paper strip at the ash pit — it should deviate towards the pit |
| Cold chimney | Insulate exposed runs; use a chimney fan on start-up |
| Blocked ventilation openings | Clear the inflow and exhaust openings |
| Soot-narrowed flue | Sweep |
| Too many bends | Re-route if possible |
| Door opened during a lean burn | Open slowly, stand to the side |
The upper door is burning (older units)
On older units a flame bumper is mandatory — the upper door will burn without it. It is a deflector that stops the heat of the flame reaching the door.
Failed fire-up
The firing-up time expired without the boiler temperature rising above shutdown temperature + 2 °C.
| Check | Detail |
|---|---|
| Fuel moisture | Aim for 20 % or below. Wet wood will not establish |
| Draft | Paper-strip test at the ash pit |
| Fan operating | Minimum speed 40 %, fan type WPA 07 / DM85 |
| Firing-up time | Range 30–120 min; MBtek value 120 min |
| Kindling | Enough to carry the load into ignition |
Boiler will not reach setpoint
| Cause | Fix |
|---|---|
| Fouled heat exchanger | Brush the top of the heat exchanger. Soot and ash reduce heat transfer |
| Scale inside the water jacket | 1 mm of scale costs 10 % of heat transfer. Check fill water hardness |
| Wet fuel | Oak at 50 % moisture carries a third of its dry value |
| Load larger than the boiler | Check the heat loss calculation against 85–205 KBTU |
| Air leaks at door gaskets | Inspect the sealing cord |
| Fan speed too low | Maximum 80 % |
Fire goes out during supervision
| Setting | Adjustment |
|---|---|
| Fan performance in supervision | Raise from 35 % |
| Pause between blowups | Shorten from 5 min |
| Purge time | Lengthen within 5–60 s |
Too long a pause extinguishes the coals; too short and the boiler temperature rises too high.
Boiler overshoots setpoint
| Setting | Adjustment |
|---|---|
| Purge time | Shorten |
| Pause between blowups | Lengthen |
| Fan slowdown threshold | Widen from 12 °C |
| Boiler hysteresis | Raise within 1–3 °C |
Room is cold although the boiler is hot
| Cause | Check |
|---|---|
| Room thermostat logic inverted | Must open when satisfied, close on demand |
| CH pump pause time too long | Range 0–240 min; factory default 1 min |
| Pump start temperature not reached | 35 °C / 95 °F |
| HUW priority stealing the heat | Turn priority off, or cap HUW working hours |
| Air in the emitters | Vent |
Pressure keeps changing
| Symptom | Cause |
|---|---|
| Pressure falls over days | Leak, or air being vented out |
| Pressure rises sharply with heat | Expansion tank undersized or waterlogged |
| Pressure rises slowly when cold | Fill valve passing |
Working pressure must not exceed 15 psi; never allow above 36 psi.
Still stuck?
MBtek technical support can help with sizing, commissioning and controller settings.
The full controller alarm list in one table.
Frequently asked questions
Parts and service
Replacing the TIS Tronic 260U fuse and sensors, the consumables not covered by warranty, and when a job must go to an accredited service centre.
Alarm codes
Complete TIS Tronic 260U alarm list with causes and resolutions — sensor errors, HUW overheating, lack of fuel, failed fire-up, emergency temperature and STB.