Is it a bad idea to tie output of hot water heater to sump pump drain?

Question

I bought a house and I have a leaking hot water heater (appliance is from 2001). I'd say it fills up an 8 ounce cup after two hot 10-15 minute showers. I had a plumber come out and he replaced the value: After a week it started leaking again. My dad came over and came up with the idea of cutting off the overflow pvc pipe from the water heater and redirecting it to the sump pump line (marked in rectangles below)

It makes sense to me - if its leaking water, redirect the water to the sump pump. I am trying to figure out if

1. This is a huge mistake and I shouldn't do it because we are not thinking of something
2. Would my water bill increase because I'd still be wasting more water than usual? I'd imagine an extra say 2 cups a day isn't that much in the grand scheme.

I figure if we replaced the water heater down the raod, we would have the undo what the PVC that we add, but that shouldn't be an issue.

Answer 1

Do not connect the overflow from the water heater to the a/c condensate line as you have marked. If the TPV ever did open wide, then water would flow back into your a/c evaporator and gas-fired furnace. This is not permitted and would be very destructive.

You could direct the output of the WH to the same pipe that the a/c condensate goes into by using the proper fittings, but if I were you I would direct my efforts to determining why the TP relief valve is leaking. What temperature do you have the WH set at? Is the water coming out of the hot water taps extremely hot?

Then I would attach an expansion adapter near the floor to the end of the pipe the condensate goes into. This would allow both pipes to feed into the pipe going to the sump and provide a visible air gap between both pipes and the pipe leading to the sump.

Answer 2

I would suggest that a TP relief valve should never leak under normal operating conditions. Therefore, since your TP valve was recently replaced with no end change in behavior, something else is going on. It looks like in your pictures you have a pressure relief tank horizontally mounted just above the inlet of your water heater. I am wondering if that expansion tank might be waterlogged or not functioning. Its purpose could be to help prevent water hammer in your pipes, or more likely in this situation since it's next to your water heater tank, that it's there to help absorb the change in water pressure due to heating of the water in the water tank.

Heating water causes it to expand, and that expanding water needs to go somewhere. If your expansion tank can't absorb and mitigate that pressure change, it tries to go into your pipes. If your water source (city/well) can't absorb the change in pressure or you have a one-way valve on your incoming water supply, if the pressure gets high enough, it will come out through your TP valve. This would be my guess as to what's happening here. So, bottom line, I suggest that you check your expansion tank and make sure it's functioning properly. How to do that, however, is something I'm not familiar with.