I need a thermostat control for a 2e440a 240v wall heater where can i get one

This has Dimplex standard wiring. You really need the full model number rather then '6900 Series'.

The search query is just three words 'make model manual' with manuAl spelled correctly. I changed it.

https://assets.sylvane.com/media/documents/products/dimplex-rdh-series-fan-forced-wall-heater-owner-manual.pdf

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depends on where the thermostat control is
normally it would plug into a control box for switching on/off of the heater by the thermostat or by a switch for manual operation

First of all most home thermostats operate on 24volts. If you want to have one that directly turns the 240 volt power on and off you need to get a special 240V line voltage thermostat. How many wires come out of your heater? Most 240v circuits have three wires. A white wire for the common and two black or black red wires that are +120 volts and negative 120 volts. That's why a 240 volt plug has 3 prongs instead of two. If you look at the wiring diagram that comes with the thermostat it should give you an idea of how to hook the wires up. In your particular case though, I think I would try making friends with an electrician.

I need a control knob for my Marley electric wall heater model#fzl3004b

Run the wire to the thermostat then to the heater

BASEBOARD WIRING WITH A SINGLE POLE (2 WIRE) WALL THERMOSTAT - 120V OR 240V SUPPLY

BASEBOARD WIRING WITH A DOUBLE POLE (4 WIRE) WALL THERMOSTAT - 120V OR 240V SUPPLY

If water is totally cold, then upper element is not getting 240V. Since element tested for 120V, then that says upper element is burned out, upper thermostat is bad, or circuit breaker is bad.
Best thing is to buy multimeter and do 30 minute troubleshoot:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

Also read information below for understanding how water heater works.

Testing elements for voltage can be misleading.
If water heater has 2 elements, then tank is 240Volts.
240V water heaters have 120V on each element at all times.
So elements have hot 120V power, but they are not turned on until the circuit is complete with 240V.
Open following links to read specifics about 120V and 240V
http://waterheatertimer.org/B220C.html
http://waterheatertimer.org/How-water-heater-thermostat-works.html

240V is made from two 120V Hot wires from breaker box.
Each 120V line from breaker is called a 'leg.'
So 240V circuit has two legs, and both legs need to be turned on to complete 240V circuit.

Water heater thermostats turn off only one leg.
The other leg is Hot all the time.
So when you test screws on an element, for example test between a screw and any bare metal part of tank, then the screw will always show 120V.
That is just one leg of the 240V circuit.
But the 240V circuit is not turned On until both legs are connected.
Every residential circuit needs two wires to complete the circuit, and in the case of 240V, those two wires are both 120V.

When the thermostat turns on, it turns on the second leg to the element and that completes the 240V circuit.
http://waterheatertimer.org/How-it-works.html

http://www.rheem.com/product.aspx?id=09DF2BDD-5E11-4D32-B574-84ACFB8A4619
http://globalimageserver.com/fetchDocument.aspx?id=052c9e32-ce37-48d7-8990-9e430f23fef3

82V80-2 Energy factor is .86 according to water heater industry self-regulated standards.

Rheem pdf says these water heaters are wired for non-simultaneous operation.
Except special order water heaters.
Non-simultaneous operation uses single 240V circuit as described below.
If your water heater is wired for simultaneous operation, and each element is on a separate circuit, that makes your water heater special order. I would guess the reason is for higher first-hour delivery, which implies rapid heating and would likely affect energy factor.
You might want to get serial number off model and call Rheem for specs on that special order.

Your water heater energy factor may be the same because 'energy efficiency is based on the amount of hot water produced per unit of fuel consumed over a typical day.' This means an aircraft carrier can be considered highly efficient despite overall cost. And naturally the guys making the aircraft carrier are also doing the rating.
http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13000

Non simultaneous operation means the upper thermostat controls heating functions.
240V goes to upper thermostat first.
When water inside tank is cold, thermostat reads temperature through tank wall.
Upper thermostat turns on upper element until top 2/3 of tank reaches thermostat set point.
Once set point is reached, upper thermostat turns off upper element and sends power to lower thermostat and lower element.
Lower thermostat reads temperature through tank wall, and turns on lower element until bottom 1/3 of tank reaches thermostat set point.
As water cools inside tank, lower thermostat is first to respond since hot water rises.
Lower thermostat turns on lower element until tank again reaches set point.
When hot water faucet is turned on, hot water exits top of tank.
At same time, cold water enters bottom of tank through the dip tube.
The heating cycle repeats.
At all times, the electricity flows through upper thermostat. And upper thermostat is powered by one 240V circuit.

With simultaneous operation, the upper and lower thermostats work in same manner.
Except thermostats are wired separately.
Lower thermostat does not wait for upper part of tank to be heated first.
Lower thermostat turns on whenever lower part of tank cools.
The advantage is more hot water available rapidly when demand is high. This is called first hour recovery.

One method for reducing electric consumption is to set lower thermostat so it only turns on during certain times of day. For example Whirlpool Energy Smart operates in this manner and shaves a few bucks off the bill each month. This says that simultaneous operation is not an energy saver, unless that circuit controlling lower thermostat is set on a timer.

If original problem was caused by sediment burning out lower element, did you clean sediment out of water heater when changing lower element?
Two element water heaters are 240V.
Thermostats cut power on one hot wire, but 240V circuit has 2 hot wires. So lower element has power at all times coming from the red wire.
1) Use ordinary tester or multimeter set to 240V <> test each screw of lower element to bare metal part of water heater. Each screw should show 120V. If there is no power, then upper thermostat is defective, screw on upper thermostat is loose, or red wire between upper and lower parts of water heater is bad.
2) Remove wires from lower element. Use continuity tester or multimeter set to ohms <> test across both screws of element to see if power travels through element <> if element is bad, then continuity tester will not light up and multimeter will show no ohms. Put wires back on element after test.
3) Start with cold water in tank. Turn on water heater & upper element will turn on. Put ear on side of tank to hear if upper element is heating water. Test #3 screw to #2 screw on low left side of thermostat, should read 240V > Test #3 screw to #4 screw on low right side of thermostat, should read 0V.
Put ear on side of tank. When upper element turns off: Test #3 screw to #2 screw on low left side of thermostat, should read 0V > Test #3 screw to #4 screw on low right side of thermostat, should read 240V. If this test shows 0V and 0V, then upper thermostat is bad. If reading is correct, immediately move to next test.
http://waterheatertimer.org/images/Thermostats-numbered-divided-500.jpg
4) Turn temp on lower thermostat to 150. Using ordinary tester or multimeter set to 240V <> Test across both screws of lower element. If there is no reading, and you know element is good from step 2, then lower thermostat is bad, or wire is bad between lower element and lower thermostat, or wire is bad between lower thermostat and top part of heater.
5) Test across both lower thermostat screws, should read 240V.If this test is good, it means wires are good. Put jumper wire across both screws of lower thermostat, and test lower element again. If element finally turns on with jumper wire, then lower thermostat is bad.
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http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html

If wire is bad between upper and lower parts of water heater, and water heater has tight-fitting 2" foam insulation, it usually indicates water heater replacement.

one set goes to your heater,,,,
red/black gr
the other set is either your voltage in, or your t-stat will control 2 units

visit this page for Lakewood parts and service center info:
http://www.lakewoodeng.com/html/parts.html