LWCO sticking on and flooding boiler multi boiler system

FitterFreds

I've got two Burnham steamers connected to a common header which has an isolation valve to separate the two systems. Used just in case one boiler goes down. Condensate for both boilers comes back to a common receiver duplex pump. One pump for each boiler. LWCO controls receiver pump for each boiler. Float in tank controls receiver level.



So the LWCO "stuck" on and flooded one boiler. Removed MM67 inspected the float and contacts. Everything is clean and function fine now. Could I be getting a vacuum from the other boiler inducing a false call on the MM67 for the other boiler? Will a vacuum breaker on the MM67 help this problem out? Has happened twice before 2 years apart. 

Steamhead

Are you using

the #67 to control the pump? If so, that's not a good idea, as the switch is not rated for such constant use. 

FitterFreds

@steamhead

Run through an iso relay

Jamie Hall

We need to know...

how the two boilers near boiler piping is hooked together.  While I don't see how you would get a vacuum anywhere in the system (unless it is a vacuum system, of course!) I can easily see how one boiler firing with the other boiler off could result in the water level in the cold boiler dropping, if the boilers aren't piped together properly.  Put simply, if the headers are open to each other, both boilers will see steam pressure, regardless of which one is firing -- but if the equalizers aren't also open to each other, it's quite possible that water will be backed out of the cold one by that steam pressure.



Piping diagram, please?

Steamhead

Problem is not the electrical load

it's that the #11 switch is not built for that kind of cycling. Remember, on pumped return the boiler may call for water every five minutes or so when firing. On gravity return it might call for water once a week.



You'll have to use a control designed for pumped-return cycling. The usual one is McDonnell & Miller's #150, which is a float-type unit mounted on equalizing piping. I believe Hydrolevel makes one that uses probes, but their site seems to be down at the moment so I can't give you any more info right now.

Long Beach Ed

#67

Steamhead is write.  If you are using a #67 switch, that is your problem. 

FitterFreds

from the factory

received an email from MM and they stated that I should use a 42s-a with an iso relay. Your thought gentlemen?