Caleffi 521400 1/2 Inch Anti-Scale Thermostatic Mixing Valve

The 521400 is the 1/2 inch nickel-plated version of the Caleffi 521 series anti-scale thermostatic mixing valve. Installed on a domestic hot-water system with storage, it blends stored hot water at 60 degrees C or more with cold water and holds the mixed outlet at a set temperature between 30 and 65 degrees C, within plus or minus 2 degrees C, despite changes in supply pressure, supply temperature and draw-off.

Why a mixing valve sits after the hot-water store

The datasheet is direct about the trade-off. To stop Legionella growth, stored water has to be kept at 60 degrees C or higher, but at 55 degrees C a partial burn takes about 30 seconds and at 60 degrees C about 5 seconds, and the times are roughly halved for children and the elderly. A thermostatic mixing valve lowers the outlet to a usable temperature and keeps it steady. The datasheet recommends setting the mixed water to no more than 50 degrees C, and notes that where the anti-scald function is required, the 5213 series is the Caleffi model to use instead.

Key features from the datasheet

• Temperature sensor fully immersed in the mixed-water outlet, with a piston sliding in a cylinder between the hot and cold channels
• Anti-scale materials for obturator, valve seats and guides with a low friction coefficient to avoid seizing from limescale
• Control knob turns 360 degrees between minimum and maximum, with a tamper-proof way to lock the set temperature
• Nickel-plated dezincification-resistant alloy body; unplated version is code 521402
• Hot (red) and cold (blue) inlets and the mix outlet marked on the body; fits in any position
• Reference test: stable mixed temperature with boiler off at 500 l/h, 3 bar hot and cold inlet pressure

Technical specification

Selection and ordering guide

The 521 series offers 1/2 inch and 3/4 inch bodies, plated or plain, and variants with strainers and inlet check valves. Choose by connection and by whether backflow protection is needed on the inlets.

The datasheet temperature table for knob positions gives about 27, 32, 38, 44, 49, 53, 58, 63 and 67 degrees C from minimum to maximum; verify on site with a digital thermometer.

Installation and commissioning notes

• Flush the connecting pipes first and fit strainers of sufficient capacity at the inlet from the mains (the 521115 and 521122 have them built in).
• Check valves are required on the inlets to prevent backflow; the 521503, 521505, 521115 and 521122 include them, while the 521400 needs them fitted separately.
• Do not couple the 521 series with boilers that produce instantaneous domestic hot water, which would impair boiler operation.
• Keep at least 5 l/min flowing for stable mixed temperature and a hot inlet at least 15 degrees C above the mixed outlet.
• Commissioning must follow current regulations by qualified personnel, with a digital temperature gauge on the mixed water.
• After setting, remove the knob, unscrew the locking screw and refit the knob on the nut protrusion to lock the value.

Applications in Gulf hotels, hospitals and housing

Domestic hot water in the Gulf is often produced by solar or electric storage tanks held at 60 degrees C or more for hygiene, so every shower bank and washbasin group needs a point where that water is blended to a safe value. The datasheet shows application diagrams with and without a recirculation circuit and with storage. Hard water leaves scale in many Gulf supplies, which is why the anti-scale construction matters. The 521 series is for single or multiple outlets, but the datasheet does not claim an anti-scald certification.

Selection and installation notes

A thermostatic mixing valve is selected from the flow, the supply temperatures and the required outlet temperature. Set the outlet temperature with the stored hot water at or above the level required for hygiene control, fit check valves and strainers on the inlets and keep the maker-specified distance to the point of use. Verify the outlet temperature with a thermometer after commissioning and after any service work.

Information needed for a quotation

Send the full model code, the quantity, the delivery location in Oman or the GCC, the intended use and any accessories needed, so that the complete package can be quoted together.

Documents and supply information

The manufacturer data sheet is attached to this page and should be read together with the project specification and the site risk assessment before a purchase is confirmed. Ratings, standards and dimensions are quoted as printed on that sheet. Lead time, stock position and certificates available with the shipment are confirmed in the quotation, and we supply to Oman and the wider GCC region for industrial, utility and building services projects.

Related items

The datasheet names the 5213 series for anti-scald duty and the pressure-reducing valve and strainer as typical items in its application diagrams. A matching Caleffi pressure reducing valve, such as the 536241 in the 5362 series, is quoted separately by exact code.

Frequently asked questions

What temperature range does the 521400 cover?

A 30 to 65 degrees C adjustable range with an accuracy of plus or minus 2 degrees C, with a lockable control knob.

What are the flow and pressure requirements?

At least 5 l/min for stable results, 5 bar dynamic and 14 bar static working pressure, and an inlet pressure ratio of no more than 2:1.

Does it include check valves?

No. The 521400 has none; the 521503, 521505, 521115 and 521122 variants include inlet check valves, and the datasheet requires check valves in the installation.

Is it an anti-scald valve?

The datasheet says that where an anti-scald function is required the Caleffi 5213 series should be used instead of the 521 series.

Who supplies the Caleffi 521400 in Oman?

Seven Star LLC is an independent supplier in Muscat and quotes against the exact code. Confirm the size, finish and check-valve needs before ordering.

Documents and quotation

The official Caleffi 521 series datasheet 01050/26 EN (2026) is linked on this page. Send the code, quantity and system type to request a quotation. See more in Hydraulic Valves & Components.