Why do we have hot water in the kitchen and laundry room, but only lukewarm in the bathrooms? We have replaced the cartridges in the bathtub and one bathroom sink. the hor water heater is turned up as high as it will go.

I do not understand what cartridges you replaced. Turn on the hot water in the tub or sink. Locate the hot water pipes in the basement and follow them as far as you can go to the bathroom. Remove the access panel to the tub and feel the pipes and also under the sink. Where exactly do you lose the hot water? When you answer this question then I should be able to give you a better answer.
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