Plumbing

Shower faucet only lukewarm even though the fixture feels hot

Anonymous user 30/09/2025 - 4:03 AM

Hi everyone, I’m having some issues with my shower and would really appreciate any advice on what might be going wrong. I’m not sure if the problem is with the water heater, the shower faucet, or possibly both. I have a thermostatic shower faucet, and it’s only giving lukewarm water. The fixture itself gets very hot to the touch where it connects to the hot water line. The hot water comes from a combi water heater (tankless unit), which is located in the same room. Sometimes the shower water even goes cold for about 10 seconds before going back to lukewarm — it seems to happen when the unit cycles off and then kicks back on. All the other hot water faucets in the condo work fine, and the heating system isn’t having any problems. Could this be a faulty cartridge in the shower faucet? Or with the water heater, could there be a build-up or cycling issue that’s causing it to shut down?