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How to regenerate a TFA hygrometer

Updated: October 2026

The parcel is open, and the first search result is a salt-jar test for a different instrument. These five TFA Dostmann hygrometers are analogue. TFA’s English note says to wrap the dial in a warm, well-wrung cloth, wait, and only then use a rear screw beside a reference. A salt test, and the half-hour towel in the 45.2028 manual, belong to other models. This guide uses the listings in the [TFA Dostmann hygrometer comparison](/hub/climate-measuring/tfa-dostmann-hygrometer). Which dial to buy is the [buying guide](/hub/climate-measuring/tfa-dostmann-hygrometer/sub/tfa-dostmann-hygrometer-buying-guide). Products Compared used TFA’s English PDF and FAQ, plus the amazon.co.uk lines from 15 October 2026. We did not run a lab. A qualifying purchase can earn us a commission at no extra cost to you.

The parcel is open, and the first search result is a salt-jar test for a different instrument. These five TFA Dostmann hygrometers are analogue.

Our top picks

TFA TFA 45.2027 indoor hygrometer

Best overall

TFA TFA 45.2027 indoor hygrometer
8.0/10about £17.39
View offer
TFA TFA 45.2045.02 indoor-outdoor hygrometer

Best value

TFA TFA 45.2045.02 indoor-outdoor hygrometer
7.9/10about £9.71
View offer
TFA TFA 45.2024 metal-ring hygrometer

Alternative

TFA TFA 45.2024 metal-ring hygrometer
7.5/10about £10.94
View offer
On this page
  1. 1.Where this listing says to put it
  2. 2.Regenerate it the way TFA describes
  3. 3.Adjust only after it has settled
  4. 4.A gap can be tolerance, and a pinned needle is a fault

Where this listing says to put it

Hang an indoor model where the bullet allows it: house, basement, or garage. That covers the 45.2024, the 45.2027, and the 45.2043.51. The 45.2041.42 is hung up for indoor climate and never adds an outdoor sentence. The 45.2043.51 also says freestanding, so a shelf is within that card. The 45.2045.02 may hang or stand, indoors and outdoors. A greenhouse question on the 45.2027 and the 45.2043.51 is not a yes. Regeneration is upkeep you repeat, not a first-day trick to force 100 %. Which movement is inside, where an English page even says, is the synthetic-hair page. The cloth is the same for an analogue TFA dial either way, and the wrong method for an electronic meter.

Regenerate it the way TFA describes

TFA’s English PDF is the method. At least every six months, wrap the dial in a warm tea towel wrung until it does not drip, for about 15–30 minutes. The pointer should then sit at about 90–99 % relative humidity. A shortfall under 90 % after a proper wrap is a reason to treat the dial as faulty, not a reason to twist the screw while it is still wrapped. The TFA FAQ uses a shorter pair: about every six months, about 15 minutes, and about 95–99 % RH. Those figures sit inside the PDF’s band. They are not a second method, and electronic meters stay on a different procedure. The 45.2045.02 says every 6 months. The 45.2041.42 says regularly and gives no interval. The 45.2024, the 45.2027, and the 45.2043.51 do not name regeneration. The PDF’s interval is TFA’s sentence for an analogue hygrometer, not a line those three amazon pages printed.
TFA TFA 45.2027 indoor hygrometer

Testsieger

TFA TFA 45.2027 indoor hygrometer
8.0/10about £17.39
View offer

Adjust only after it has settled

Take the wrap off and leave the dial in room air beside a reference for 30–45 minutes. Only then use the rear cross-head screw. Turning it in the towel sets the pointer against wet cloth. On the 45.2024 the rear slot can be hard to see. After the wait, a living room near half scale is an ordinary result. The cloth target, about 90–99 %, applies only while the towel still affects the movement. A printed comfort band of 40–60 % is not that target.

A gap can be tolerance, and a pinned needle is a fault

TFA’s FAQ allows two thermometers, each inside ±1 °C, to differ by 2 °C and both stay in band. The 45.2024, the 45.2041.42, and the 45.2027 print ±1 °C. The 45.2045.02 prints ±2 °C. The 45.2043.51 prints both 1 °C and ±2 °C, and both lines stay. A 2 °C gap can be that stacking. These listings do not print a humidity tolerance such as ±3 % RH. A pinned or tangled needle is a fault. UK reviews describe that on the 45.2024, plus a rattle on the 45.2041.42 and a pointer stuck at 100 % on one 45.2045.02 review. Two UK reviews are not most owners. A unit that arrives not working is a satisfactory-quality question under the Consumer Rights Act 2015, section 9, taken up with the seller. When the problem is the building, the damp and mould page says when to stop.

Common questions

How does TFA say to regenerate an analogue hygrometer?
Wrap it in a warm tea towel wrung until it does not drip, for about 15–30 minutes, at least every six months, until the pointer sits at about 90–99 % RH. Air it for 30–45 minutes, then use the rear screw. Leave the screw alone while it is wrapped, and do not use this cloth on an electronic TFA meter.
How often, if the listing does not say?
The 45.2045.02 says every 6 months. The 45.2041.42 says regularly, with no interval. The other three listings do not name regeneration. TFA’s English PDF still says at least every six months for an analogue hygrometer. That note is not a sentence those three amazon pages printed.
What should the pointer do after the cloth?
After a proper wrap it should sit at about 90–99 % RH. A reading of 100 % is the wrong expectation. Once the dial has aired, judge it against the room. A pointer that stays pinned in ordinary air is a fault to raise with the seller.
When do I touch the rear screw?
After the wrap is off and the dial has sat in room air beside a reference for 30–45 minutes. The screw is the rear cross-head. Turning it during the towel sets the movement while it is still wet. If the slot is hard to find, look before you push.
Is a salt jar the TFA method?
No. TFA’s English PDF describes the warm, well-wrung cloth, then the wait, then the screw. A salt jar is the generic method. The half-hour wet towel in a 45.2028 manual belongs to the 45.2028, which is not one of these five.
My two dials differ by 2 °C. Is that a fault?
It can be tolerance. Two instruments each within ±1 °C can differ by 2 °C and both stay in band. The 45.2045.02 prints ±2 °C, and the 45.2043.51 prints both 1 °C and ±2 °C. A needle that arrives pinned is a different problem, under the Consumer Rights Act 2015, section 9.

Related pages

Best TFA Dostmann hygrometer

TFA Dostmann hygrometer

Which TFA Dostmann hygrometer to buy on amazon.co.uk

Hygrometer damp and mould: when to heat, air, or stop

TFA synthetic hair hygrometer: which page names it

Sources

Manufacturer and public UK sources used for this comparison. Listing prices, stars, and review counts are from amazon.co.uk on 15 October 2026.

  1. TFA — English hygrometer instructions (retrieved 16 October 2026)
  2. TFA — thermo-hygrometers (retrieved 16 October 2026)
  3. TFA — frequently asked questions (retrieved 16 October 2026)
  4. TFA — analogue thermo-hygrometer 45.2027 (retrieved 16 October 2026)
  5. TFA — analogue thermo-hygrometer 45.2043 (retrieved 16 October 2026)
  6. Centre for Sustainable Energy — temperature and humidity at home (retrieved 16 October 2026)
  7. GOV.UK — damp and mould in the home (retrieved 16 October 2026)
  8. Consumer Rights Act 2015, section 9 (retrieved 16 October 2026)