Shaking heater is Hayward H4001DL - Hayward Pool & Spa

Not enough water flow!
Either a

• bypass valve is open all the way, and reducing water flow into heater
• Worn/broken internal bypass - unitherm governor
• Blockage of some sort reducing water flow, in circulation line

When something like the above is present, the minimal water flow, gets super heated really fast when heater is on and firing! So hot in fact, that the water turns to Steam Instantly!
and the steam is a very Volatile substance! Remember? It was once used to move Locomotives!
get this fixed asap!
call a pool / spa professional for assistance in evaluating your next step.

Good Luck.

is this heater is been install for above the ground pool it will be better either way to use a hard schedulle 40 pvc to prevent any checking in the hoses for future leak ,is the heater connections are correct in and out , mean from the return the filter go to inlet side the heater them the outlet side of the heter (HOT WATER) GO TO RETURNS of the pool ? also check if the pump got full prime not air,is the filter is clean? also check for any brocken parts inside the flowvalve control, after years low PH AND TA will destroy internal parts in heater include leaking heater exchangers.

I'm assuming that you have checked the water circuit and have bleeded it correctly and thoroughly - air bubbles will cause that when they go thru the heat exchanger.
The banging and shaking are caused by the blower from the burner- it's either:
1 - the motor is dislodged from its casing and the blades of the propeller fan are hitting the case walls - the casing will have to be opened and the motor refitted properly;
or
2 - the bearings of the shaft of the motor of the blower are damaged and the shaft oscillates - the entire blower will have to be replaced, here's a new one - number 2http://www.poolpartsonline.com/p-11-hayward-h100id1-h100idp1-above-ground-heater-parts.aspx
or
3 - the propeller is loose on the shaft - the blower will have to be dismantled and the propeller reattached .
Here is an exploded diagram to help you with the dismantling
http://www.poolpartsonline.com/popup.aspx?src=wolthuis.aspx%3fproductid%3d11%26size%3dlarge

Is it leaking? Has anything shaken loose inside? If you can get it to light the cause and fix for the banging and shaking is here: https://sites.google.com/site/haywardpoolheater/
Takes about 30 minute and you are done, but you have to figure out what else has gone wrong to stop it lighting

Check your water flow and make sure your by-passes are set to send water threw the heater. That is to say shut off. The water in the heater is over heating and the clunking is the water turning to steam.

The bypass assembly inside of the header has failed. It will need to be replaced. I would also replace the internal thermostat while you are in the header.

You can try to get a welding shop to tack it back in place (I do not remember who to credit for that but it was not my suggestion) and see if it stops.

The exchanger is expensive as a DIY part...about $350...but if that is all that is wrong it is a lot cheaper than $700+ for a whole new unit.

Stop using the heater immediately. You are boiling the water inside and this can lead to a dangerous situation if a limit switch fails to act in time.

You will likely find the diverter in the inlet side of the heater is broken. You are looking for a stainless steel plate in the water path. If you can move it by hand, it is broke. It is not replaceable and requires a new heat exchanger assembly to repair it.

Your part number is IDXHXA1101. We sell it as will most pool dealers. If you would like a quote, contact us at www.arrowmotor.net

Actually, the clicking is likely causing the shaking. Inside the manifold of a H100 is a stainless steel diverter plate that send some of the passing water into the heat exchanger and lets the rest past and back to the pool. When it breaks, you will hear a 'clicking' noise at it rattles in the water path. When it breaks, the flow to the heat exchanger is intermittent and you will begin to boil the water, causing the shaking. This situation is dangerous, especially without a pressure relief in the heater or pipe. As long as your water chemistry is sound, Hayward will usually cover this under warranty even if the unit is over a year old. Contact them to get a factory authorized repair rep out at: http://www.haywardnet.com/locator/

see this link ....

http://www.fixya.com/support/t1078177-hayward_pool_heater_h_series