Horne Engineering Ltd
Issue 3 8/05
5
5.3 The frequency of in-service testing depends upon the condition of water passing
through the TMV. In-service testing must be carried out more frequently in hard
water areas than in soft water areas. As a general guide, in-service testing should be
carried out at intervals somewhere between 6 months and 12 months. In-service
testing should be carried out at least every 12 months and, where the water is hard,
the interval may be less than 6 months. Experience of local conditions and the in-
service testing record will dictate the frequency of in-service testing.
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MAINTENANCE
6.1 Maintenance of all Thermostatic Mixing Valves is essential. If a TMV does not
operate properly, there is a risk of someone being scalded. The frequency of
maintenance depends upon the condition of the water. The remarks in 5.3 regarding
in-service testing apply equally to maintenance.
6.2 "O" ring seals should be replaced at least every 3 years.
6.3 The THERMOSTAT ELEMENT (6) should be replaced at least every 6 years. All
other parts should be replaced only if physical damage has occurred.
6.4 MAINTENANCE PROCEDURES
6.4.1 Close hot and cold water inlet isolating valves and open pipework to allow
pipework to drain.
6.4.2 CLEANING STRAINERS - Unscrew END CAPS (16) and withdraw STRAINER
BASKETS (14). Clean the baskets and descale them, if necessary.
THERMOSTATIC MIXING VALVE MECHANISM. Minor maintenance can be
carried out with the HORNE 25 in situ :-
6.4.3 Unscrew VALVE COVER (3). Remove THERMOSTAT ELEMENT ASSEMBLY
(6), SLIDE VALVE ASSEMBLY (7) and RETURN SPRING (8).
6.4.4 The SLIDE VALVE ASSEMBLY (7) is a precision part and must be handled with
care.
6.4.5 Remove the ADJUSTING SCREW (2) by turning it clockwise until the thread
disengages.
6.4.6 The SLIDE VALVE SEAL (9) can be removed by piercing the rubber with a sharp
pointed probe. Take care not to bruise the edges of the groove.
6.4.7 If the SLIDE VALVE SEAL (9) has been removed, then it MUST be replaced with
a new one. NEVER re-use an "O" ring.
