Can I get energy credit for heat pump installed 12/23? I paid 3,133 so far on installment plan, but still owe about 14,000.

If the heat pump was installed in 2023 you needed to enter it on your 2023 tax return, enter the original cost of the pump when it was installed.  You can amend the 2023 tax return to add the heat pump as a tax credit.

See this TurboTax support FAQ for amending a prior year tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-already-filed/L4VjJ9BA2_US_en_US?uid=ld1n99kr

You claim the item in the year it is installed (placed in service, turned on) even if you are paying over time.   If you can't use the entire credit in the first year, it will carry forward.  

The pump would have to meet or exceed the "Consortium for Efficiency (CEE) highest efficiency tier" to qualify as energy efficient property. The paperwork included in your purchase documents may help you determine if it qualifies. You can learn more from this IRS article.