Weil-McLain 550-141-850/0599 manual Is thermostat circuit closed continuity across wires?

Part number 550-141-850/0699

•Installation • Start-Up • Parts • Maintenance

CHART 8 — Insufficient heat or no heat to system (POWER light on steady)

Electrical shock hazard — Wherever you see ▲ TURN OFF POWER▲ , follow the instructions. Failure to follow instructions could result in severe personl injury, death or substantial property damage.

• Has it been at least 5 minutes since setting thermostat to

Is boiler System circulator operating?

call for heat? If not, wait 5 minutes. Is system heating?

No

Yes

• Is thermostat set to call for heat? Remove thermostat

wires at boiler and check continuity across the two wires.

If circuit isn't closed, check external thermostat (zone

•

Remove CIRCULATORS harness plug from

valve, relay, etc.) wiring. Correct problems and retry.

CIRCULATORS plug receptacle (Figure 34, Item

• Reconnect external thermostat wiring at boiler.

4). Check with voltmeter across left-side 120 VAC

Is thermostat circuit closed (continuity across wires)?

N and 120 VAC H pins of receptacle.

Does voltmeter show 120 VAC across pins?

No

Yes

No

Yes

Are all red lights off?

•

Replace control

•

Repair/replace

• Boiler is in standby.

No

Yes

module.

circulator. Retest.

• Set thermostat to call for heat

•

Retest.

•

Repair/replace

and recheck operation.

wiring. Retest.

• Verify Sequence of operation,

Wait 30 seconds.

Figure 22.

Are all red lights off?

No

Yes

•

Wait 5 minutes.

Is FLAME light on?

No

Yes

Replace control module.

Retest.

• If you have sufficient heat — boiler should be in normal

• Check block switch on top of boiler with continuity

operating sequence. (See normal sequence of operation,

checker.

Figure 22.)

Are block switch contacts closed?

•

If you have less than sufficient heat —

No

Yes

Is vent or combustion air piping free of blockage?

No

Yes

• Wait for cast iron block to

• Check limit switch

contacts with continuity

cool to room temperature.

•

Correct conditions and

checker.

Contact your Weil-McLain

Are block switch

recheck operation.

Are limit switch

sales representative.

•

See Figure 22 for

contacts closed?

contacts closed?

normal sequence of

operation.

No

Yes

Yes

No

• Wait for boiler water to cool to temperature 20 to 30 ˚F

lower than temperature set on limit switch.

Are limit switch contacts closed?

Replace block

Replace control

Replace limit

No

Yes

switch. Retest.

module. Retest.

switch. Retest.

•

Boiler water temperature exceeded setting on limit switch

• Excessive block temperature has been reduced to safe

operating level. Check for low water level or mineral

with thermostat calling for heat. Boiler is OK. (See normal

deposits in sections. Correct before proceeding.

sequence of operation, Figure 22.)

• Restart boiler and check normal sequence of operation.

•

Also check operation of setting on limit switch (should be

(See normal sequence of operation, Figure 22.)

above 140˚F.).

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