2001 chevy blazer. no heat! changed thermostat, put new hoses in filled with antifreeze still not hot?

when i took the hoses off and put them back on I had heat for about 10 minutes then it went back to cold
2001 chevy blazer. no heat! changed thermostat, put new hoses in filled with antifreeze still not hot?
You have caused an air lock in the heater matrix by changing the thermostat and hoses. When you drain water out, it is replaced by air. To cure this, take off the cap for the radiator filler, and start the engine, and rev it up slightly until the temperature gauge reaches the normal position. Now you need to have someone standing by with radiator coolant, and watch the water level in the rad filler suddenly disappear. They have to top up the rad, while you keep the engine running, more air bubbles will appear and the water level will drop again. Keep topping up and run the engine until no more air bubbles appear, Job Done.
2001 chevy blazer. no heat! changed thermostat, put new hoses in filled with antifreeze still not hot?
Please do not remove the radiator cap while the vehicle is running, this is not safe. If the air pocket is trapped in front of the thermostat, when it purges it can spray hot coolant out the radiator filler hole. At 180 to 200 degrees.

The easiest way the get the air out of the coolant system. is to park on an incline facing up or jack up the front of the vehicle. The reason for this is becuse the heater core and thermostat housing sit just higher then the radiator fill when the vehicle is on a flat level surface.

Now, slowly remove the radiator cap and top off the coolant level. You will notice air starting to bubble out of the filler neck. Continually to top off the coolant until no bubbles are present. Now place the palm of your left hand over the filler neck to seal the radiator, with your right hand squeeze the upper radiator hose close to the thermostat housing. You will feel coolant raise up against your palm and as you release the hose you will fill the fluid level drop. Do this twice, remove your hand off the filler neck and top off coolant level. This step will take several attempts to get most the air out. Also work your way up the hose with each top off. Once no more air is visible and the level is at the inner rim of the neck, install the radiator cap, fill the over flow bottle to about 3/4. This will be important as the engine cools down.

Start the vehicle and let idle. Turn off all accessories to include the heater and blower. Watch as the temperature gage increases. Once the gage reaches 1/2, turn on the heater with the fan on low speed. Watch the gage as it raises to just below 3/4, this is when the thermostat should open and the gage temp. drop slightly. You should now notice an increase in passenger compartment heat.

Turn off the vehicle and feel both heater hoses, they should both feel hot, but the smaller return will feel just slightly cooler. If both are hot, you have purged the air out of the system.

What usually happens when the coolant system is disturbed, an air pocket can develop under the thermostat causing it not to open. The thermostat, temp. sensor, and temp. switch need to be submerged in fluid to operate properly.

Take your time and be careful. Under no circumstance do you every purge a coolant system with the radiator cap off, unless you are wanting to get 2nd and 3rd degree burns.

Hope this helps and good luck. Christopher
Possible Air Bubble in system. Start the car and let it idle and make sure the temperatur control on your heater is all the way to the hot side. When it gets up to temperature, the thermostat will open and let water through the system. Have the Radiator cap off, and watch the level. You will probably have to top it off before you finish. But remember, have your Temperature control all of the way to hot with the heater on.
could be the heater core is plugged up/ sometimes the door that switches back and forth between heat and cool (heater core-a/c coil) stops working. listen down under the dash while someone works the control from cool to hot and see if you can hear the door moving back and forth. sometimes (depending on car) you can tell if the control feels different, like it has no resistance when you move it back and forth, there should be some. to check the heater core remove the hoses under the hood and see if water will flow thru it by placing a hose on one and flushing water thru out the other one. if its plugged completely it must be replaced but partially plugged you might be able to flush it out.
An air pocket will be the most likely culprit. There are other scenarios that apply

here and just a month ago we had one with the same symptoms as yours and we

purged and bled with always the same results.... then we discovered the heater

blend door had a cracked plastic gear. The blend door (not the mode doors) was

Ok once we replaced the plastic gear and the heater worked like a champ! This

was kind of tricky to find and I hope it may help!
Flush or replace heater core. solved
heater core plugged up back flush it might clear it some most likey needs replacing

remove heater hose flush water thru heater core both way a few minutes try again