| First, the tempering valve may well be required by code, so you do not want to mess with that. It is a safety item, to prevent scalding. Now, check your temps and your numbers. 120º is too hot to shower in. (see chart below). You would mix a little cold in with that. If you cannot get water at about 105 to 110, then maybe the tempering valve needs to be adjusted.
TIME / TEMPERATURE RELATIONSHIPS IN SCALDS
125° F 1 1/2 to 2 minutes
130° F About 30 seconds
135° F About 10 seconds
140° F Less than 5 seconds
145° F Less than 3 seconds
150° F About 1 1/2 seconds
155° F About 1 second
Table courtesy of Shriners Burn Institute |