# Water heater T&P valve dripping due to pressure spikes—root causes & fixes **URL:** \ **Category:** Trade Talk\ **Tags:** diy-se\ **Created:** [August 12, 2025, 11:31am UTC](https://home.renovation.reviews/t/water-heater-t-p-valve-dripping-due-to-pressure-spikes-root-causes-fixes/20487 "2025-08-12T11:31:20Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![reno\_questions](https://home.renovation.reviews/user_avatar/home.renovation.reviews/reno_questions/32/2758_2.png) [@reno\_questions](https://home.renovation.reviews/u/reno_questions)\ **Post date:** [August 12, 2025, 11:31am UTC](https://home.renovation.reviews/t/water-heater-t-p-valve-dripping-due-to-pressure-spikes-root-causes-fixes/20487/1 "2025-08-12T11:31:20Z")
AO Smith power-vent 50-gallon water heater equipped with an ST-5 expansion tank; the T&P valve drips when there are pressure spikes. What steps can I take to troubleshoot possible PRV problems, assess thermal expansion, and determine the appropriate size and charge for the expansion tank? ---
**Author:** ![Joyboy03j](https://home.renovation.reviews/user_avatar/home.renovation.reviews/joyboy03j/32/2900_2.png) [@Joyboy03j](https://home.renovation.reviews/u/Joyboy03j)\ **Post date:** [August 13, 2025, 11:58am UTC](https://home.renovation.reviews/t/water-heater-t-p-valve-dripping-due-to-pressure-spikes-root-causes-fixes/20487/2 "2025-08-13T11:58:33Z")
Check the PRV for proper function and pressure setting, measure static and spike pressure to confirm thermal expansion, then size and pre charge the expansion tank to match system pressure. ---
**Author:** ![BuildersLTD](https://home.renovation.reviews/user_avatar/home.renovation.reviews/buildersltd/32/14872_2.png) [@BuildersLTD](https://home.renovation.reviews/u/BuildersLTD)\ **Post date:** [August 13, 2025, 11:59am UTC](https://home.renovation.reviews/t/water-heater-t-p-valve-dripping-due-to-pressure-spikes-root-causes-fixes/20487/3 "2025-08-13T11:59:16Z")
Very good response, thank you! ---
**Author:** ![Theodore\_3456](https://home.renovation.reviews/user_avatar/home.renovation.reviews/theodore_3456/32/2821_2.png) [@Theodore\_3456](https://home.renovation.reviews/u/Theodore_3456)\ **Post date:** [August 13, 2025, 12:10pm UTC](https://home.renovation.reviews/t/water-heater-t-p-valve-dripping-due-to-pressure-spikes-root-causes-fixes/20487/4 "2025-08-13T12:10:16Z")
Pressure spikes are often from thermal expansion or high incoming water pressure. First step, test your water pressure with a gauge (should be 50–60 psi). If it’s high, install a pressure reducing valve and an expansion tank. If those are already in place, the T&P valve may just be worn out and need replacing. ---
**Author:** ![Bobby\_Michael](https://home.renovation.reviews/user_avatar/home.renovation.reviews/bobby_michael/32/2057_2.png) [@Bobby\_Michael](https://home.renovation.reviews/u/Bobby_Michael)\ **Post date:** [August 13, 2025, 12:33pm UTC](https://home.renovation.reviews/t/water-heater-t-p-valve-dripping-due-to-pressure-spikes-root-causes-fixes/20487/5 "2025-08-13T12:33:54Z")
The T&P valve dripping during pressure spikes might be related to the expansion tank or water heater settings. I’d recommend checking the expansion tank’s pre-charge pressure and ensuring it’s properly sized for your system. ---
**Author:** ![Bobby\_Michael](https://home.renovation.reviews/user_avatar/home.renovation.reviews/bobby_michael/32/2057_2.png) [@Bobby\_Michael](https://home.renovation.reviews/u/Bobby_Michael)\ **Post date:** [August 13, 2025, 12:36pm UTC](https://home.renovation.reviews/t/water-heater-t-p-valve-dripping-due-to-pressure-spikes-root-causes-fixes/20487/6 "2025-08-13T12:36:07Z")
I’m feeling you lad, you really got this ---
**Author:** ![Tim\_Michael1](https://home.renovation.reviews/user_avatar/home.renovation.reviews/tim_michael1/32/6294_2.png) [@Tim\_Michael1](https://home.renovation.reviews/u/Tim_Michael1)\ **Post date:** [August 13, 2025, 12:54pm UTC](https://home.renovation.reviews/t/water-heater-t-p-valve-dripping-due-to-pressure-spikes-root-causes-fixes/20487/7 "2025-08-13T12:54:34Z")
> [@reno\_questions](#): > > AO Smith power-vent 50-gallon water heater equipped with an ST-5 expansion tank; the T&P valve drips when there are pressure spikes. What steps can I take to troubleshoot possible PRV problems, assess thermal expansion, and determine the appropriate size and charge for the expansion tank? Your water heater’s relief valve might open because the water pressure spikes. This often happens if the pressure-reducing valve (PRV) isn’t working well. Or your expansion tank may be too small or doesn’t have enough air. To solve this, check that the PRV keeps the pressure steady and that the expansion tank fits your system and has the right air level. If the PRV is bad, fix or swap it out. A bigger expansion tank or adding air to the current one should stop the leaks if that’s the issue.