Or "heating service" (servicio de calefacción).
Leaving aside the "fnarr" factor, "hot" is sometimes used as a synonym for "live", in electrical wiring contexts. In the absence of sufficient context to decide on the best term, I'd be strongly tempted simply use the literal translation. It could refer to the boiler system for the provision of hot water or steam as mentioned, or electrical installations, air conditioning/central heating…

Suggestion: "servicio caliente" > "hot operation" / or "hot operating environment")

Power Piping - NRCwww.nrc.gov › docsPDF
Pressure-Temperature Ratings for Piping Components . .11. 102.3 ... Table A-8, Temperatures 1200°F and Above. ... Boilers, of the ASME Boiler and Pressure Vessel Code, ... Section which most nearly applies to a proposed piping ... interruption in the normal physical structure of material ... ture, are defined as follows:.

Process Manual - Rockwoolwww.rockwool.com › rti-brochure-process-manual_na_enPDF
engineers and construction supervisors optimum ... temperature alternates above or below the ambient ... piping operating below ambient temperatures ... by insulation, apply additional protective ... Observation: The table shows the corrosion of the “material”, and not that of the “ ... ASME "Boiler and Pressure Vessel Code".


Wilo-Rexa PRO cms.media.wilo.com › wilo182787
PDFTranslate this page
is above 85 dB(A) and an indication made in the work regulations! 2.9. Maintenance work ... To avoid injury, allow the motor to cool down to ambient temperature be- fore commencing work! ... type of system: Alternating operation or parallel operation. ... ADVERTENCIA. Escaldaduras por material de servicio caliente.


Domestic Central Heating Wiring Systems and Controlsbooks.google.com.jm › books
If the temperature of the water exceeds the high—limit setting at any time the safety ... return to normal operation. temperatures then the link—fuel boiler is switched off. ... Water is supplied to the slumber (b) Temperatures above the low—limit set— ... (c) Any requirement for heating or ***hot Operation** of the system is switched ...
Ray Ward - 2005 - ‎Technology & Engineering

Environmental Health Series: Air pollutionbooks.google.com.jm › books
The study indicates that changes in ambient temperature result in significant changes in ... 1.4-5 and can be applied between 20 and 80°F. For temperatures outside this range, ... The 1975 FTP measures emissions over three types of driving: a cold ... factor represents 20 percent cold operation and 80 percent ** hot operation.***




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Note added at 42 mins (2020-05-12 17:50:26 GMT)
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https://cms.media.wilo.com/dcidocpfinder/wilo182787/1607384/...
Page 87: Advertencia
Escaldaduras por material de servicio caliente

Due to a lack of context by Asker, it could also be dealing with fluids too, and therefore, the answer depending on additional context, if provided, could relate to "hot operating fluids" (applies to operating temperatures above room temperature).

It appears in a boiler and pressure vessel construction
Page 40: Scalding due to hot operating fluids!
When the pressure escapes, hot operating fluid can also be ejected. This can result in
scalding! To avoid injuries, the following instructions must be observed

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Note added at 56 mins (2020-05-12 18:04:52 GMT)
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Lucía: We've all asked for additional context, please! You would be advised to give us more context, as you now have two proposals from Michael and myself, but we are operating in a vacuum here. Please note that all questions you ask here on this forum, must contain proper context! We cannot work "in isolation" and then you expect us to give you proper assistance. Thanks so much for "listening" to my spiel; I fully appreciate you are new, but those are the published guidelines of this forum. A please and thank you won't hurt either.

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Note added at 1 day 7 hrs (2020-05-14 00:59:40 GMT) Post-grading
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Lucía: So, are you now saying, as I have seen Helen Chavarria's reference and your note to her that the term you seek is "Puesta en servicio caliente/arranque"? I am a tad confused as we have all pleaded for some additional context, i.e. discussion box asking you if you would post a few lines before the required term and a few lines after, so this leaves me a bit confused. Anyway, here is what I just found for you:

I did find this a moment ago and refers to the "Hot start up" (arranque), e.g. of a boiler system: *** denotes portion I wish to highlight to you.


THERMAL POWER PLANT A-Z: boiler technical termspowerplanta2z.blogspot.com › 2016/07 › boiler-techni...
Jul 29, 2016 - So if the design pressure is 100 KPa(g), the hydrotest pressure would be 130 ... In a Boiler fuel is burnt to get heat energy which is converted from ... Start-up of Boiler within 2 Hrs of Tripping of Boiler is known as the *** Hot Start-up of Boiler.*** 1. ... 8. Super heater temperature has to be maintained with the help of ...

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Note added at 1 day 7 hrs (2020-05-14 01:01:45 GMT) Post-grading
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https://powerplanta2z.blogspot.com/

And another one: (hot start)

THERMAL POWER PLANT A-Z: Power Plant Operationpowerplanta2z.blogspot.com › 2015/07 › power-plant-...
Jul 14, 2015 - Maintenance section has to request in writing the operation section for ... Commissioning seal oil system ... Gassing up operation take long hours (5-6 hours). ... Warm or **hot start** of the machine is required when the unit is stopped for few ... precaution must be taken to expel all the air from boiler tubes while ...

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Note added at 1 day 9 hrs (2020-05-14 02:24:53 GMT) Post-grading
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Hi Lucía:

I too truly understand everything you said in light of Helen's contribution! I do also realise that you gave us as much information as you had trying to contextualise the meaning of "servicio caliente" which is what you originally posted! I do understand. [I had suggested perhaps a few phrases before, whether dealing with "servicio caliente" or not may have also helped colleagues to contextualise it too (but perhaps not). I also recognise how difficult it must be for you to keep trying to tell us all there is no more context, but there was nothing ontoward intended in our repeated requests, except our wish to help you. That is all! The only thing I keep asking myself is whether it is just "water" alone or "fluids" as a whole, and why I posted what I posted. Anyway, Lucía, the matter is now closed, and you've made your decision, and I try to abide by the Asker's decisions, as ultimately the work is yours, not ours! Regards.