Cleaver Brooks Boiler CB-700-150

1mamba

Boiler fires up but it struggles too make set point which is 180, no leaks discovered,would low gas pressure cause this

Jamie Hall

1mamba said:

Boiler fires up but it struggles too make set point which is 180, no leaks discovered,would low gas pressure cause this

Among other things. You need someone with the proper test instruments to come out and check the gas pressures all the way through the train, and also check combustion air and draught -- and, most likely, thoroughly clean the fireside of the boiler. Should be done annually.

Mike_Sheppard

Is it modulating to high fire? It may be stuck in low fire. Lots of CB boilers have a low fire hold aquastat that prevents the boiler from going to high fire until the boiler warms up to 140 degrees. But if it dips below that during the winter the load may exceed low fire input causing the boiler to become stuck in low fire.

Something else that happens occasionally is someone will put the manual/auto switch to manual and set to potentiometer to closed meaning it will stay at low fire.

Put the manual auto switch to manual. Turn the potentiometer to open (high fire) once the boiler is up to operating temp put the switch back to auto.

Sometimes people mistake the low fire hold aquastat for the operator Aquastat and set it for 180 along with the operator. Meaning the boiler will never go to high fire.

I run at least several emergency calls each winter for these issues.

You need to have a professional come check your settings and make sure that boiler is operating safely.

If you are located in the VA, MD, DC area feel free to contact me.

I work on Cleaver Brooks boilers almost daily. From 125hp to 1,500hp.

EBEBRATT-Ed

@1mamba

What @Mike_Sheppard said

Watch the mod motor when the boiler starts. It should move toward high fire almost as soon as the burner motor starts. Then after the high fire purge it drives to low fire then you get the gas pilot ignition and then main flame. After main flame lights the flame safeguard control releases the burner to modulate on water temperature if the controls Mike Sheppard mentioned are set correctly