Dom Estic Hot Water Mode; Frost Protection; Low Water Pressure Sensor (I Nternal) - UTICA BOILERS MAHF-75 Installation, Operation And Maintenance Manual

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W ARN I N G
Burn, Scald Hazard! Wat er t em perat ure over
125° F ( 51° C) can cause severe burns and
scalding. See User's Manual before set t ing wat er
t em perat ure. Failure t o follow t hese inst ruct ions
could result in deat h or serious inj ury.
1 0 .4 Dom est ic H ot W a t er M ode
Com bi Boilers – M odels 1 1 5 , 1 5 0 & 2 0 5
• Dom est ic hot wat er call for heat is init iat ed when a
faucet is opened and water flow is sensed by boiler's
DHW flow switch.
• 3- way valve divert s boiler wat er t o dom est ic hot
wat er ( DHW) heat exchanger ( Brazed- plat e) t o heat
incom ing dom est ic wat er.
• Com bust ion fan com e on at ignit ion speed, closing
t he air pressure swit ch ( 150 m odel only) , allowing
power to flow to the spark generator and gas valve,
creat ing ignit ion in t he com bust ion cham ber.
• Flame sensor senses flame in combustion chamber
and sends a signal t o t he cont rol board.
• Cont rol board m onit ors boiler wat er and
DHWt em perat ures, m odulat es fan speed and gas
rat e accordingly.
• Dom est ic call for heat ends when faucet is closed
and DHW flow switch does not see water flow.
H ea t Only Boilers – M odels 7 5 , 1 0 0 & 1 2 5 w it h I ndirect
Ta nk
• When t he boiler receives a call for hot wat er from
t he I ndirect t ank Aquast at or Tank Sensor, t he
3- Way valve divert s wat er from t he heat ing syst em
t o dedicat ed I ndirect t ank supply t o heat dom est ic
wat er in t he t ank.
• Com bust ion fan com es on at ignit ion speed, closing
t he air pressure swit ch ( 125 m odel only) , allowing
power to flow to spark generator and gas valve,
creat ing ignit ion in t he com bust ion cham ber.
• Flame sensor will sense flame in combustion
cham ber and send a signal t o t he cont rol board.
• Cont rol board m onit ors boiler wat er and DHW
t em perat ures and m odulat es fan speed and gas rat e
accordingly.
• Call for dom est ic wat er heat ing ends when t he
aquastat or tank sensor is satisfied.
H ea t Only Boiler 1 6 5
165 boiler does not have a 3-Way Valve. When
paired wit h an I ndirect t ank, t he t ank is a separat e
heat zone. The Indirect tank is controlled by a field
supplied m ult i zone relay, priorit y is det erm ined by
t he relay set t ings.
1 0 - OPERATI N G I N STRU CTI ON S
1 0 .5 Frost Prot ect ion
Boiler m onit ors supply and ret urn wat er t em perat ures t o
enable frost prot ect ion which aut om at ically t urns boiler
and pum p on.
I f wat er in boiler falls below 41° F ( 5° C) , providing boiler
is connect ed t o power, boiler will operat e unt il wat er
t em perat ure in t he syst em reaches approxim at ely 86° F
( 30° C) .
Frost prot ect ion is for boiler only and not for com plet e
Cent ral Heat ing Syst em .
1 0 .6 Pum p
I f elect ricit y is connect ed t o t he boiler, regardless if
power is "On" or "Off" and has not operated for 24
hours for heat ing or hot wat er, boiler pum p will operat e
aut om at ically for one m inut e every 24 hours.
1 0 .7 Low W a t er Pressure Sensor ( I nt erna l)
This device prot ect s prim ary exchanger from dam age.
I t will not allow boiler t o run in a LOW wat er pressure
sit uat ion. Low wat er condit ion occurs when wat er
pressure drops below 7.0 psi ( 0.5 bar) .
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240013503 REV A, [ 03/ 15/ 2022]