When does God refuse to hear our prayers?

Jeremiah 11:11

God sees, hears and knows everything—including our prayers. Nothing escapes his attention. Why then did God say he would not listen to the people’s cries for help? There are several possible reasons.

In this case, God did not respond because judgment was unavoidable. Judah had disobeyed God’s laws and ignored his pleas for so long that judgment was, in effect, already on the way. Their cries were too little, too late. God even told Jeremiah not to pray for the people (see Isa 14:11–12)—that not even Moses and Samuel could have persuaded him to offer further compassion to them (see Isa 15:1).

It’s also possible that people sometimes sabotage their own prayers. The Bible mentions actions that can short-circuit our prayers

1.sin

If I had cherished sin in my heart, the Lord would not have listened; --- Psalm 66:18

But your iniquities have separated you from your God; your sins have hidden his face from you, so that he will not hear. --- Isaiah 59:2

This is what the Lord says about this people: “They greatly love to wander; they do not restrain their feet. So the Lord does not accept them; he will now remember their wickedness     and punish them for their sins.”  Jeremiah 14:10-12

2.disobedience

If anyone turns a deaf ear to my instruction, even their prayers are detestable. --- Proverbs 28:9

3.hypocrisy and insincerity

The Lord says: “These people come near to me with their mouth and honor me with their lips, but their hearts are far from me. Their worship of me is based on merely human rules they have been taught. --- Isaiah 29:13

By offering defiled food on my altar. “But you ask, ‘How have we defiled you?’ “By saying that the Lord’s table is contemptible. When you offer blind animals for sacrifice, is that not wrong? When you sacrifice lame or diseased animals, is that not wrong? Try offering them to your governor! Would he be pleased with you? Would he accept you?” says the Lord Almighty.  “Now plead with God to be gracious to us. With such offerings from your hands, will he accept you?”—says the Lord Almighty. --- Malachi 1:7-9

4.wrong motives

And when you pray, do not be like the hypocrites, for they love to pray standing in the synagogues and on the street corners to be seen by others. Truly I tell you, they have received their reward in full. But when you pray, go into your room, close the door and pray to your Father, who is unseen. Then your Father, who sees what is done in secret, will reward you. ---

Matthew 6:5-6

The Pharisee stood by himself and prayed: ‘God, I thank you that I am not like other people—robbers, evildoers, adulterers—or even like this tax collector. I fast twice a week and give a tenth of all I get.’ “But the tax collector stood at a distance. He would not even look up to heaven, but beat his breast and said, ‘God, have mercy on me, a sinner.’  “I tell you that this man, rather than the other, went home justified before God. For all those who exalt themselves will be humbled, and those who humble themselves will be exalted.” --- Luke 18:11-14

When you ask, you do not receive, because you ask with wrong motives, that you may spend what you get on your pleasures. --- James 4:3

5.lack of faith

And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him. --- Hebrews 11:6

But when you ask, you must believe and not doubt, because the one who doubts is like a wave of the sea, blown and tossed by the wind. --- James 1:6

6.marital problems

Husbands, in the same way be considerate as you live with your wives, and treat them with respect as the weaker partner and as heirs with you of the gracious gift of life, so that nothing will hinder your prayers. --- 1 Peter 3:7

7.prayer may actually be a delayed

Then he continued, “Do not be afraid, Daniel. Since the first day that you set your mind to gain understanding and to humble yourself before your God, your words were heard, and I have come in response to them. But the prince of the Persian kingdom resisted me twenty-one days. Then Michael, one of the chief princes, came to help me, because I was detained there with the king of Persia. --- Daniel 10:12-13

8.Other times God may deny our request in order to give us something better than what we knew to ask for.

Source : Bible Gateway. Questions Answered section

www.biblegateway.com