Bradford White U2TW75T*RN, Service Manual

Page: 31 / 40

U TTW S ERV I CE PROCEDURE X
Safety Circuit Voltage Trace
Safety C ircuit V oltage T race
W AR N I N G
11 5 volt potential e x posure. Use caution
m akin g volta g e checks to avoi d personal injur y .
P o s ition g a s c ontrol s wit c h to the “ON”
po s ition and ad j u s t thermo s tat dial to c all
for heat , I s there 10 to 1 3 VAC between red
wire leadin g to blower temperature s wit c h
and g reen g round wire ?
B lower mu s t be runnin g durin g thi s
v olta g e c he ck
(s ee photo 2 6).
Red wire leadin g to
blower temp . s wit c h
G reen g round wire
2 6
Y ellow wire
leadin g from
pre ss ure s wit c h
Y
I s there 10 to 1 3 VAC between y ellow wire
leadin g from pre ss ure s wit c h and g reen
g round wire
(s ee photo 2 6) ?
D o y ou hear or c an y ou s ee
the i g niter s par k in g?
Y
Y
I s L E D on g a s v al v e fla s hin g the
“ heartbeat ” c ode ( alternatin g
bri g ht / dim )
N
Safet y c ir c uit
v olta g e i s O K .
N o v olta g e from g a s c ontrol ,
c all for te c hni c al s upport .
Y
NO T E: T hi s p r oc e du r e a ss um e s a cool t a nk.
V erif y 11 5 VAC to g a s
c ontrol (s ee pa g e 32 ).
I s there c ontinuit y
throu g h blower
temperature s wit c h
(s ee pa g e 24 ) ?
Y
C he ck for loo s e or
bro k en wire c onne c tion
at s wit c h terminal s.
N
N
D etermine c au s e of blower
temperature s wit c h a c ti v ation
and c orre c t .
C he ck i g niter /s en s or
(s ee pa g e 19).
i s i g niter /s en s or O K?
If burner doe s not li g ht ,
ob s er v e L E D fla s h c ode on
g a s v al v e and refer to
trouble s hootin g s e c tion on
pa g e 1 2 .
N
N
P a g e 3 1
25
S t e p 1. R e mov e t h r ee s c r e w s (Phillip s
Sc r e w d r iv e r ) f r om con tr ol
a cc e ss cov e r on blow e r a nd
r e mov e cov e r ( s ee pho t o 2 4
a nd 2 5).
F ault y c ord s et or
g a s c ontrol .
Y
C orre c t i g niter /
s en s or problem .
C ontrol Acc e ss
C o v er S c rew s
24
R
31