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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Vaillant GA 100 boiler for my radiant baseboards.

Customer Question

Hi I have a Vaillant GA 100 boiler for my radiant baseboards. It works fine but the water temp coming out of my faucets is over 140. Way too hot. I tried turning down the thermostat on my regular hot water heater tank but that didn't make any difference. That makes me think I need to lower the thermostat on the boiler but I can't see where to do it. Any suggestions ?
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: I think it's working fine but I can't see where to lower the temp.
JA: Do you plan on doing the work yourself?
Customer: Yes if it's a simple adjustment
JA: Anything else we should know to help you best?
Customer: Don't think so
Submitted: 6 months ago.
Category: HVAC
Expert:  Phil replied 6 months ago.

Hello, the problem is that the mixing valve (tempering valve) on your hot water tank has the cold water supply pipe valve closed to it, OR its stuck in the wrong position.

Lowering the boiler temperature would work, but not very well, as that temperature cycles 10 degrees hi and lo, and if you set it to 120F you are likely to find the boiler water is not hot enough to heat the house.

Get me the brand and model number of the mixing valve that you are adjusting, we can go from there.