Hydronic heat safety switch

[gayler]

My system was put in nearly 25 years ago by a company that was new to hydronic. There were several things designed wrong. One is the lack of a safety to turn off the gas in the event of pressure loss in the system. I would like to add something to turn off the gass if the heater loses liquid due to a leak. What would be needed for this? I’m running a 50 gallon natural gas water heater. I’m assuming a pressure switch to control a solenoid valve on the gas line?

 

[PCustoms]

Is that a normal control in modern systems?

 

[u3b3rg33k]

Boiler low water cut out (LWCO) controls are a pretty common thing.
Mine won't fire at all until it's over 7.3 PSI, and won't fire at full rate until it's over 13 PSI.

 

[Firebrick43]

They use discrete low water cutoffs near the high point in the system. If you can’t get it installed in the highest point it needs to be at least above the boiler.

Modern modcon boilers have one built in

Hydro level low water cut off

 

[PWC Repair]

Mine is a low pressure switch tied into the low voltage thermostat controls. If it gets below 5 psi (closed loop liquid loss) it opens the circuit so no matter what the thermostat tries to do.....nothing will come on.

 

[fitter30]

Are you questioning a boiler or a stand alone water heater?
Hot water boiler above 400k btu's low water cut off is required. If its a water coil or tube it's protected by flow switch.
Stand alone water heater is protected by a relief valve set at 210°f and or 150lbs
Thermocouple protects gas valve from opening if pilot flame isn't detected. Being connected to city water or well if there is a leak the leak would be pressurised unless the water would be off and tank would drain and gas valve thermostat would also fail.

 

[gayler]

Are you questioning a boiler or a stand alone water heater?
Hot water boiler above 400k btu's low water cut off is required. If its a water coil or tube it's protected by flow switch.
Stand alone water heater is protected by a relief valve set at 210°f and or 150lbs
Thermocouple protects gas valve from opening if pilot flame isn't detected. Being connected to city water or well if there is a leak the leak would be pressurised unless the water would be off and tank would drain and gas valve thermostat would also fail.

50 gallon natural gas water heater. If the heater drains due to a leak wouldn’t the thermostat still fire the burner? This is a closed system with antifreeze and water.

 

[gayler]

On a related note. My expansion tank is leaking. It is a 6 gallon tank, 50 gallon water heater, five loops in the floor and 1200sq ft garage. I’m not sure if I really need a tank that size. Is this the correct size for my garage?

 

[PCustoms]

50 gallon natural gas water heater. If the heater drains due to a leak wouldn’t the thermostat still fire the burner? This is a closed system with antifreeze and water.

So?

I don't see a safety risk here

 

[PWC Repair]

On a related note. My expansion tank is leaking. It is a 6 gallon tank, 50 gallon water heater, five loops in the floor and 1200sq ft garage. I’m not sure if I really need a tank that size. Is this the correct size for my garage?

Sounds a bit large. My system is almost just like yours. I believe my tank is a 2.5 or 3 gallon. You don't need a very large tank for the lower pressures of a small (ish) closed loop system. I only run 5-10psi pressure in mine.

 

[gayler]

Sounds a bit large. My system is almost just like yours. I believe my tank is a 2.5 or 3 gallon. You don't need a very large tank for the lower pressures of a small (ish) closed loop system. I only run 5-10psi pressure in mine.

Thanks! That’s what I was thinking too. The company that did it used a six gallon tank and the biggest I can find is 4.5.