FAQ
TL;DR: A 25-40-180 circulator moves up to 3.5 m³/h and “the pump is cooled with water and without water it could seize” [Elektroda, DUDAŚ, #9079562; Elektroda, Piotr77777, #9080215]. Boiling usually spares the boiler, but a dry-running pump or blocked vent can fail. Why it matters: Knowing the weak spots avoids another midnight melt-down.
Quick Facts
• Circulator 25-40-180: 0.2–3.5 m³/h flow, 3.8 m head, +2 to +110 °C fluid [Elektroda, DUDAŚ, post #9079562]
• Blower WPA120: 255 m³/h airflow, 345 Pa pressure, 75 W input [Elektroda, DUDAŚ, post #9079562]
• Max system pressure: 10 bar (spec plate) [Elektroda, DUDAŚ, post #9079562]
• Pump prices: budget ~100 PLN; Grundfos ≈220 PLN [Elektroda, Piotr77777, post #9085002]
• Polish PN-91/B-02413: ≥12 l expansion per kW heat load [PN-91/B-02413]
1. Why did the pipe insulation and controller cables melt?
Steam leaving the boiler exceeded 100 °C; surface temperatures near the flue often hit 140 °C before pressure lifts the safety lid. Typical foam insulation softens above 90 °C, so it deformed first, then radiant heat attacked nearby PVC cables that soften at 80 °C
[Elektroda, DUDAŚ, post #9079562]
2. Is it normal for a solid-fuel boiler to boil?
Manufacturers allow occasional boiling; cast-iron sections tolerate 110 °C if pressure is relieved
[Elektroda, Piotr77777, post #9079803] Frequent boiling points to undersized radiators, excessive fuel load, or blocked circulation.
3. What fails inside a pump that ran dry?
Water lubricates and cools the ceramic plain bearing. After 3–5 min dry, friction can seize the rotor and warp the sleeve
[Elektroda, stanislaw1954, post #9081875] Grundfos tests show rotor temperature above 180 °C after 10 min dry run [Grundfos, 2020].
4. Why does the boiler gauge read 78 °C while the controller shows 60 °C?
Melted insulation separated the sensor from the hot pipe, so it measures cooled air, not water. Re-strap the probe with metal tape and add 10 mm mineral wool around it
[Elektroda, stanislaw1954, post #9081641]
5. How do I safely refill and bleed after a boil-over?
- Let the fire die and switch the pump off. 2. Open the fill valve slowly until water drips from the open vent. 3. Bleed radiators top-down, then restart the pump [Elektroda, Piotr77777, post #9079803]
6. Should the circulator sit on the flow or the return line?
7. Is my ball valve ruined after overheating?
The brass or steel ball survives. Only the PTFE seat can deform above 180 °C. If the handle turns smoothly and the valve seals, leave it; replacement 1" valve costs 15–100 PLN
[Elektroda, Piotr77777, post #9085002]
8. How can I confirm the pump is seized?
Unplug, remove the front screw, and spin the impeller with a screwdriver. No movement means seizure. “If some muck has entered the impeller, cleaning may revive it”
[Elektroda, Piotr77777, post #9085002]
9. Which replacement pump offers best value?
10. Can the system run by gravity if I remove the pump?
Yes, provided pipe slopes are continuous and valves fully open. Users reported heat reaching distant radiators after 20 min, though flow is only 20–30 % of pumped rate
[Elektroda, DUDAŚ, post #9085344]
11. Why are the radiators farthest from the boiler lukewarm?
A slowing or seized pump reduces differential pressure, so branch losses dominate. Switching to speed III raised their temperature immediately
[Elektroda, DUDAŚ, post #9083195]
12. What causes gurgling at 65–75 °C?
Rapid firing heats the grate faster than water flow removes heat, forming steam bubbles. Ensure pump runs before the blower ignites and avoid dumping coal all at once
[Elektroda, stanislaw1954, post #9196531]
13. Will the open-vent expansion tank freeze in the attic?
14. What happens if both radiator and DHW valves stay closed while firing?
With no circulation, heat has nowhere to go; pressure relief lifts, water sprays, and air enters, leaving the pump dry—exactly the failure seen in 2024 posts
[Elektroda, julka2010, post #21028490]
15. Edge case: can a circulator give an electric shock after overheating?
Generated by the language model.
