SUNLU FilaDryer S4 Pro: problems, parts and running costs
Checked: 2026-10-20
Summary
Most of what goes wrong with the S4 Pro is a limit rather than a breakdown: it tops out at 85 °C, so PETG parts cannot be annealed in it, and each of the two zones is 220 mm deep, which rules out 2 kg spools. SUNLU publishes no temperature-accuracy figure, no warranty length and no independent test for this model, so the parts to budget for over the years are the feed-through tubes and the spool-holder bearings, on top of filament and electricity for a 380 W heater. The second zone is the only functional reason to pay the premium over the single-zone S4; $139.99 (SUNLU Official Store, October 2026) is defensible, and below $120 it is strong value. [1][4][5]
Common problems and fixes
- Annealing stops at 85 °C — SUNLU confines its own annealing mode to materials and printed parts with an annealing temperature of 85 °C or less, and trade coverage puts PETG annealing at roughly 90-110 °C, so PETG parts cannot be annealed in this box. Workaround: dry PLA, PETG, TPU, ABS, ASA, PA, PC and carbon- or glass-fiber-filled variants as usual, and use the annealing mode only on PA, PC and PP parts. Not a warranty matter. [1][2][5]
- Two 220 mm zones, so 2 kg spools do not fit — the S4 Pro splits the chamber into two zones of 220 × 210 × 211 mm, half the 450 mm depth of the older S4’s single chamber, so the 4 × 1 kg figure is a capacity claim rather than a 2 kg claim. Workaround: run four 1 kg spools, two per zone, and check spool width before buying 2 kg spools. [1][4]
- No published temperature accuracy, and no independent test — SUNLU publishes no ± figure for the S4 Pro while publishing ±3 °C at 70 °C and ±5 °C up to 110 °C for the E2, and no instrumented test of this model was found. Zone-to-zone difference, warm-up time, sound level and measured power draw are all unknown. Workaround: measure both zones with your own thermometer before committing a multi-day filament batch. [1][5][6]
- The humidity cycle is described vaguely — the listing says the system starts when internal humidity reaches the set level and stops at 25% RH, without saying how it behaves against the 30-50% target, while the older S4’s page spells the cycle out. Workaround: set the target and confirm the reading with an external hygrometer. [1][4]
- Feed-through tubes and spool bearings wear — the box ships two 1 m PTFE tubes, eight stainless steel shafts and sixteen bearings, which is a two-bearing-per-spool mount, so tubing and bearings are the parts that fail over time. No spare-parts catalogue or service manual was found and the printed manual has no located digital version. Workaround: keep spare tubes and bearings on hand and order them through SUNLU support. [1][4]
- Warranty length is not published — the store’s after-sales policy gives 14 days for refund and return in new, unused condition, a 30-day exchange window, and then warranty as the only recourse, with eight categories of damage excluded including misuse, third-party repair, non-quality issues after 30 days and purchases without proof of purchase. That policy covers SUNLU Official Website purchases only, so a buyer through a marketplace or reseller has to deal with that seller. The adjacent S4 is published at one year with exclusions for non-original power supplies; treat one year as a working assumption until the S4 Pro warranty text is read. [3][4]
- No owner history at all — no owner report, forum thread or retailer Q&A for this exact model was found, so every statement about its behaviour comes from SUNLU’s own copy. Check the unit on arrival against the published figures: 380 W rated input, 4.7 kg net weight, and two zones that each reach the set temperature. [1][6]
Parts and consumables
- Filament — the recurring running cost; SUNLU’s shop attaches a “from $40.95” figure to bundle options carrying 1-3 kg of filament (October 2026). [4]
Yearly running cost
The dryer is rated at 380 W, but SUNLU publishes no duty cycle, measured draw or energy-use figure, so the electricity part of a year’s running can only be estimated from the cycle you set yourself. On top of that come the consumables, PTFE feed-through tubes and spool-holder bearings, and the filament itself; SUNLU’s shop lists bundle options carrying 1-3 kg of filament from $40.95 (October 2026). No price for a spare tube or a bearing set was found in the sources, so no reliable yearly total can be stated. [1][4]
When it is a good buy
- At or below $120: strong value — under the single-zone S4’s $116.99 at the SUNLU shop (October 2026) and near the $100 Creality Plus Space Pi benchmark in 3DPrint.com’s February 2025 price roundup. [4][5]
- $121-140: defensible — SUNLU Official Store sits at $139.99 for the US plug (October 2026), and the premium over the single-zone S4 is about $23; the second independently controlled zone is the only functional reason to pay it. [1][2][4]
- $141-160: weak to fair — the EU-plug variant already sits at $149.99 (October 2026), and at that level the $249.99 FilaDryer E2 at SUNLU Official Store (October 2026) is worth costing out for its 25 °C of extra headroom, published accuracy and UL, CE, FCC, UKCA and ROHS certification. [1][2][5]
- Above $160: poor value — nothing in the readable record justifies paying more while the 110 °C alternative sits at $249.99 with published accuracy and certification. [2][5]
Alternatives: the single-zone SUNLU FilaDryer S4 at $116.99 (SUNLU shop, October 2026) when you dry one material type and never anneal; the SUNLU FilaDryer E2 at $249.99 (SUNLU Official Store, October 2026) when you need 110 °C for PETG annealing or want published accuracy and certification; the Creality Plus Space Pi at $100 (3DPrint.com, February 2025) when the 85 °C ceiling and the second zone do not matter. [2][4][5]