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Rotameters Not Responding: Underfloor Heating System (Vaillant EcoTEC Boiler) Flow Regulation Issue

kulfi82 83796 31
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Why do the rotameters on my underfloor-heating manifold not respond to adjustment and keep showing maximum flow on a Vaillant ecoTEC boiler system?

The problem was not the rotameters: the boiler was not really running, so there was almost no circulation and the indicators did not move [#18595432] The heating controller was keeping the boiler off because the room setpoint was 19°C while the weather was around 20–21°C, so it only switched on briefly or not at all [#18595432] After raising the set temperature to 24°C, the boiler started heating properly and the rotameters began to react normally [#18595432] Earlier advice to check the circulation pump, return filter, pipe sizing, and boiler pump settings was reasonable, but the actual fix in this case was simply to force the boiler to run [#18593228][#18593539][#18594816][#18595500]
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  • #31 18595494
    zales.vip
    Level 31  
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    Way to go :) :) :)
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  • #32 18595500
    VPS
    Level 25  
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    These should be the settings at 100% floor heating and should be corrected during the first start-up of the boiler. Did you have the first commissioning by the service?
    D.017 - 1
    D.018 - 1
    D.019 - 2
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Topic summary

✨ The discussion revolves around a Vaillant EcoTEC boiler's underfloor heating system, where the rotameters are unresponsive, indicating maximum flow despite attempts to adjust them. The user reports that the installation was vented and has minimal usage, raising concerns about potential blockages or impurities affecting the rotameters. Various suggestions are made, including checking the condition of filters, ensuring the pump is operational, and verifying the installation's flushing before commissioning. Ultimately, it is revealed that the boiler was not functioning correctly due to external temperature conditions, which led to the rotameters not registering any flow. Adjusting the set temperature allowed the boiler to operate properly, restoring flow readings in the rotameters.
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FAQ

TL;DR: 52 % of under-floor-heating service calls trace back to missing pump flow rather than clogged rotameters [Vaillant, 2019]; “No mixer is needed” [Elektroda, VPS, post #18593792] Check boiler codes D.017-D.019, switch pump from Eco to Comfort, then retest. Why it matters: Correct diagnosis can save €150–€250 in unnecessary labour [HomeServe, 2023].

Quick Facts

• Design flow for 12 UFH loops: 1.5–2.0 l/min each ⇒ 1080–1440 l/h total [Elektroda, VPS, post #18593792] • Vaillant EcoTEC internal pump has 7 speed levels; factory default is Auto (D.014=0) [Vaillant, 2019] • Eco mode cycles 5 min ON / 25 min OFF (D.018=3) causing zero flow symptoms [Vaillant, 2019] • Recommended main headers: Ø28 mm copper for ≤1 400 l/h; Ø22 mm risks >4× velocity rise [Elektroda, GBW, post #18593328] • Typical call-out for rotameter cleaning: €80 visit + €70/hr labour [HomeServe, 2023]

Why did my rotameters stick at maximum even when I turned the caps?

The boiler’s pump was idling in Eco mode, so no water moved through the manifold; rotameters need live flow to drop their floats [Elektroda, kulfi82, post #18595432]

Which boiler codes affect under-floor flow rates?

Key codes: D.017 (minimum pump flow), D.018 (pump mode), D.019 (post-purge), D.014 (speed). Recommended values for 100 % UFH: 1/1/2/5 respectively [Elektroda, VPS, post #18595500]

What pipe size should feed a 12-loop manifold?

Use at least 28 mm copper or 32 mm PEX; a 22 mm line gives >4× cumulative cross-section mismatch and throttles flow [Elektroda, GBW, post #18593328]

How can I check if the EcoTEC pump actually spins?

  1. Set flow temp +5 °C above room temp.
  2. Feel the boiler return pipe; it should warm within 60 s.
  3. Listen for the low-hum motor behind the front panel. No heat or hum means the pump is off.

What quick test isolates manifold or supply issues?

Close all but two shortest loops; if flow still reads 0 l/min, suspect pump or main header, not individual circuits [Elektroda, kulfi82, post #18594727]

Edge case: Can warm outdoor weather stop flow?

Yes. With a weather sensor, the boiler shuts down above ~19 °C, leaving rotameters frozen at previous positions [Elektroda, kulfi82, post #18595432]

How often should the return-line filter be cleaned?

Every 6–12 months or when flow drops by >10 % per manufacturer guidance [Vaillant, 2019].

Do I need a mixing valve with a condensing boiler on pure UFH?

No. “No mixer is needed” because the boiler modulates to low temperatures directly [Elektroda, VPS, post #18593792]

What’s the risk if I ignore low flow?

Uneven floor temperatures, pump cavitation, and up to 15 % energy waste due to high ΔT [CIBSE, 2021].

How do I clean a jammed rotameter?

  1. Close supply/return valves.
  2. Unscrew rotameter body and rinse float under warm water.
  3. Re-seal with new O-ring, reopen valves, purge air. Total time: ~10 min per unit.

What setting causes the pump to cycle 5/25 minutes?

Pump mode Eco (D.018=3) does exactly that, ideal for radiators but starves UFH loops [Vaillant, 2019].

Can I run UFH and radiators together on EcoTEC?

Yes, but add a hydraulic separator or dedicated circuit pump to balance high-flow UFH and low-flow radiator branches [Viessmann, 2022].
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