Understanding my system - Mixing valves

fgamache

As I learn to use and configure my radiant heat system properly, I was reading about mixing valves and the need for a minimum return water temp to avoid corrosive condensation. Currently the mixing valves (manual type) for my two zones are fully open.

Tx151C boiler with SS exchanger (from what I can tell), no specs from manufacturer. Boiler temp is set to 37C (100F).

Any input from the pros?

EBEBRATT-Ed

Your boiler is a condensing type so water temperature as low as 86 degrees will do no damage to the boiler. It looks from the picture that you are also heating your domestic hot water from the boiler. Radiant systems operate at 120 deg or below. To make DHW your boiler needs to run at a higher temp. Mixing valves prevent the boiler from overheating the radiant zones when the boiler temp is higher than normal (such as on a DHW call)

GroundUp

There are no mixing valves in that system, and that boiler LOVES low return temps. During a DHW call, DHW is prioritized so there will never be overheating of the radiant zones during a DHW call. The radiant uses the 100 degree water from the boiler during heat calls, and the two knobs I'm assuming you are calling mixing valves, are simple pressure bypasses to prevent the pumps from dead-heading if the actuators are not yet open. Nothing to worry about!

fgamache

GroundUp said:

There are no mixing valves in that system [...] and the two knobs I'm assuming you are calling mixing valves, are simple pressure bypasses to prevent the pumps from dead-heading if the actuators are not yet open. Nothing to worry about!

Great, thanks for the clarification! Seems I have more to learn than I thought lol.

hot_rod

Those bypass valve do need to be adjusted properly.

By hand you could open all zones, put your hand on the bypass pipe, you should not feel any flow/ temperature in the bypass.

Turn a zone or two off and the valve will start to open and bypass. Directions should be with the valve, or online. Rare that one is full open.