Install Instructions
Troubleshooting
Under normal operating conditions the Caleffi 521 thermostatic mixing valve will provide a very high
level of performance. However, in some circumstances, where the following maintenance schedule
is not followed problems may arise.
Recommended maintenance schedule:
Tests should be conducted regularly to monitor the thermostatic mixing valve performance, as
deterioration of performance could indicate that the valve and/or the system require maintenance. If,
during these tests, the temperature of the mixed water has changed significantly in comparison with
the previous test, the details given in the installation and commissioning sections should be checked
and maintenance conducted.
The following should be checked regularly to ensure that the optimum performance levels of the
valve are maintained. Check every 12 months at least, or more often if necessary.
1) Check and clean the system filters.
2) Check that any check valves positioned upstream of the Caleffi thermostatic mixing valve are
operating correctly, without problems caused by impuritites.
3) Limescale can be removed from internal components of the thermostatic mixing valve by
immersion in a suitable de-scaling fluid.
4) When the components which can be maintained have been checked, commission the valve.
Radiant panels heating system
Item
Description
Item
quantity
per valve
1/2 inch 3/4 inch 1 inch
NPT
521400A, AC
521410A, AC
Sweat
521409A, AC
521419A, AC
NPT
521500A, AC
521510A, AC
Sweat
521509A, AC
521519A, AC
Press
521506A
521516A
NPT
521600A, AC
521610A, AC
Sweat
521609A, AC
521619A, AC
Union
washer
3 F50055
Union
n u t 1"
3 F61008 F61008
Male
tailpieces
3
R31981
(2 only – “410”)
NA10002
(2 only – “419”)
31901A
(2 only – “510”)
NA10003
(2 only – “519”)
NA16265*
(2 only
– “516”)
59817A*
(2 only – “610”)
59834A*
(2 only – “619”)
Inlet male
tailpiece
with check
valve –
“AC” mod-
els only
2 59893A 59904A 59840A 59905A — 59894A 59906A
Outlet
tailpiece –
“AC” mod-
els only
1 R31981 NA10002 31901A NA10003 — 59817A* 59834A*
Outlet
adapter
with tem-
perature
gauge
1 NA10358** NA10328 NA10358** NA10056 NA10358** NA10358** NA10058
1 688003A
*Tailpiece fitting with integral union nut. 1" NPT and Sweat models require only two separate 1" union nuts (F61008).
**NA10358 requires additional parts. Choose appropriate tailpiece, washers, and union nut to complete the adapter.
Replacement fittings