My ignition has failed to start the heater, like its not clicking over. I need it fixed. Do I need to call someone out or can it be fixed by me????

bad regulator. might need a repairman to come out. or you can replace the regulator yourself.

I’m happy to help further over the phone at https://www.6ya.com/expert/david_92c86cbc79e9b552

If Clicking, then most likely the heater is looking for "Fuel" to ignite!
Also, ... if the heater is clicking, sparking, then the heater has received all the confirmation to ignite, no need to check for switch in ON position, or thermostat/heat setting up enough, or sensors or ??? If they had failed, then NO clicking! So again, it is now looking for fuel for main ignition.
check the gas valve, is it on?
check the main gas shut off, on?

When was last time the heater ignited? If recently just prior to non operation, then the gas valve had possibly failed? It is not opening to allow the main burner to ignite. do you have a flame at the pilot? If so, then all of the above checks are not necessary, hence if valves were off, NO flame at pilot assembly! If no Flame, then check the valves for gas supply.

My guess without being there to diagnose, bad gas valve.

The picture shows a Pentair Heater, this is the valve for that.
but they are all very similar.

This system will not have a pilot light, instead it will have an electronic ignition or hot surface ignitor. The problem can be a number of things. You can check to see the operation of the unit by having someone turn the thermostat on while you are at the unit and go from there. The order of operation will be:
Inducer draft motor starts (small motor in heat compartment), after the motor runs and pulls the pressure switch in, telling the furnace that its safe, it then starts the ignitor. This will either sound like a clicking noise until the pilot lights or there will be a orange glow by the burners, after a few seconds, the gas valve calls and the burners should ignite.
By doing this, you can get more information to what the problem actually is. If your unit fails to start the inducer draft motor, fails to call for ignitor, fails to call at gas valve, fails to stay on after ignition. Your system should have a control board with LED trouble lights also. If you can see blinking lights, count the number of times they blink, then look for a trouble code chart, usually on the back of a panel. Hope this helps!

Change the flame sensor if you have clean it with sandpapers twice . steel wool is much better to use than sandpaper.

Are you sure that your gas supply is strong enough, and that being said is there an in line regulator on your installation? You need gas pressure along with volume to burn properly. The itself sounds fine it is going thru all of its system checks then shutting down. You need someone with a set of gauges and check gas line pressure then check past the regulator and again check the pressures. It could be as simple as opening the regulator up slightly or as costly as replacing the line with a bigger one to support the heater. Make sure that you have purged the line good, and I would do this at the dirt leg in the supply or as close to the heater as possible.

C3 is a common error that simply means there is no flame. There are many reasons for a "no flame" situation. You must troubleshoot the heater to find why. Start with the simple stuff like taking the air pump pressure to find out if the problem is fuel related or electronics related. Then repair as needed.

Click on the links below. Maybe this info will help you get started.

Check the air pump pressure


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change presure switch , no quick fix

Make sure propane is on and getting to your stove burners ok, first, then try switching it back on. If it fails to ignite, shut switch off and try a couple of times, if still no ignition, get back to me.

Sounds like starter motor or there is a switch for the gearbox this does fail