Problems with Floe Drain Down

I have a Bailey Autograph that uses the whale adapter fresh water filler system. I recently tried to fully drain the water system using the Floe Whale Drain Down device to pressurise the water system and blow excess water.

I emptied the system first including dumping the water in the boiler.

I connected the Floe device to the water filler and then tried to pressurise the system to 15psi. I got as far as 6.5psi and found the system would not pressurise any further. I checked that all the taps and dump valve were closed but no joy.

I contacted Floe who replied;

"First, let's look at our kit. Some caravans, try to push the whale adapter back out of the wall, when entering pressure. Try to hold the block in firm and read the gauge to see if it helps. You might want someone inside draining the taps first

Next let's look at your own setup. The most common issue for losing air pressure is at the dump valve for the water heater. Try lifting (or get someone) the dump valve up a fraction and see if it closes the valve. The valve is designed to be pushed down with one finger, so it snaps closed. If you use your thumb and forefinger, it can push the lever down too far, lifting the back hinge out of the floor again. By lifting up slightly, this can close it better. Only a hair's breadth though."

I've not had chance to try this yet and just wondered if anyone else had experienced this problem or had any thoughts on what I may be doing wrong.

Thanks in anticipation.