Carpet cleaning foam

The heater is likely clogged with soap gunk. The water for the upholstery tool does not go through the heater in you model. You can sometimes get it running again by putting vinegar in the tank and trying to flush it through and get it to dissolve or flush out the obstruction. It can take a few days or weeks of leaving the vinegar in the machine. Usually the obstruction must be removed by taking the heater out and cleaning it. The heater is in the handle. You can unscrew the handle and separate the front and back to access the heater.
If you can get the water flowing again you can keep it from happening again by not putting soap in the machine. Some models will not dispense water without something in the soap tank but you can put in water. If you put soap in the machine it is spraying the soap and water on to the carpet and immediately extracting it back out, it will still clean but not as well as if you would allow a few minutes dwell time to soften and loosen the oily sticky soils.
The best way to clean a carpet is by using a pre-conditioner (basically the soap) mixed into hot water and sprayed onto the carpet after it had been thoroughly vacuumed to remove as much dry soil and debris as possible. Allow a few minutes dwell time and flush out with fresh clean water. Your carpet will be cleaner and stay clean longer because you got it cleaner but also you rinsed out the soap.
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If you are using the correct shampoo then the tank my need to be replaced. They will clog if tank wasn't cleaned after last used. Check that the dial is open and both filters are in place , add water and shampoo and test without the hose connected . If you still have no suds coming out then just order a new tank.

White streaks might be soap residue, get carpet slightly wet and agitate it to see if it foams up. It may dpneed to be rinsed out.

A good place to start is the owner's manual. If you don't have one, you can google the make and model of your multi-vac to get another copy.

Most wet-vacs work off the same principle. Pre-vacuum the carpet to make sure there is not normal surface dirt and dust. Next Squirt on hot soapy water, scrub it in - then suck up the dirt and collect the dirty water.

So after vacuuming the area to be wet-vacuumed and you are lucky enough to have a separate reservoir on the wet-vac unit - add pre-mixed carpet cleaner into hot tap water (with carpet cleaner mixed into it by the ratios described on the carpet cleaner soap bottle) to the multi-vac water reservoir (from a quick look, the Delonghi doesn't have one) . With the settings for wet vac (per the owners manual), squeeze the trigger for applying the carpet cleaner. Typically, you will go slower than normal vacuuming. Give it a chance to soak in and dissolve/lift the grim and dirt. Come back slowly to pull the dirty water out of the carpet.

There are multi-wet vacs (like the M31) that don't have a reservoir for the carpet cleaner. In that case, you need to pre-mix a couple of gallons of carpet clean in a separate container or bucket. Next spray or sprinkle carpet cleaner onto/into the carpet. Try to scrub the cleaner into the carpet to really get at the dirt and lift it. Next is to vacuum up the wet stuff.

Some carpet cleaners do not contain an anti-foaming agent. I recommend you either add an anti-foaming agent or buy a carpet clean product that already contains it - otherwise, it tends to be a big mess that takes a lot more time.

I hope these tips help.

There are a few things that can cause a Bissell carpet cleaner to not dispense water. First thing to check is the belts if your machine is a Pro Heat. The flat belt goes around the motor shaft and the pump. As the motor runs it spins the pump. This is a stretch belt and stretch belts should be replaced at least once or twice per year to work properly as they will lose elasticity even if the machine has never been turned on. The first thing to check is to see if water will spray from the upholstery tool. If it sprays but you still get no water at the floor jets then check and clean the jets to insure they are not clogged. Getting water from the upholstery tool means the pump is working ok. If not, make sure the water tank and soap tank are not empty. Even if the water tank is full make sure the soap tank is full too. I would suggest NOT putting any soap in the soap tank because that is what causes most of the problems. Put plain tap water in the soap tank and try the machine again. Hold the trigger down giving it plenty of time to flush out any air bubbles and/or soap from the pump and the lines. If you still can't get any water from to the floor jets the most likely problem is the heater is clogged with mineral deposits or soap gunk. When a machine sits in the closet for months the soap in the lines coagulates and will clog things up. Which is why if you want the machine to work for a long time NEVER put soap in it. To do a better job of cleaning put your soap and hot water into a sprayer and use this solution to pre-condition the carpets. Pre-conditioning gives the soap and hot water a chance to dissolve the gunk in your carpets, then use fresh hot water in the machine to flush the soap and dirt from your carpets. Your machine will last longer and your carpets will be cleaner and stay clean longer because you rinsed out the soap. If you try this method you will be amazed how much cleaner your carpets will be.
If you need to clean the heater you will need to separate the handle assembly by removing all the screws. First make sure the machine is unplugged. You'll have to figure out which screws need to come out, it's not too tough. The heater is inside the handle. Look at how it comes apart so you will know how to put it back together. The heater is the silver metal thing with wires and hoses. Remove the screws that hold the cover on being sure not to lose any of the tiny red gaskets. Remove the cover and clean the soap or mineral deposits from the heater core, put the cover back on and put it back together and it should work fine. To keep it from getting clogged again simply make sure you use soft water if minerals were the problem and never put soap in the machine.

After cleaning is finished, Rinse out any left over soap from solution tank.
Refill with two cups of cool clean water and add two tablespoons of apple cider vinegar Braggs works great run trigger until all solution is spent.
No more clogged jets. Hope this helps..

Try changing the water before you turn it on the first time -- that will probably help you resolve the issue. It seems like there is probably some sort of soap or carpet shampoo in the system causing your foam issue. If your carpets have been shampooed or if you have spilled soap or detergent on your carpet at any point, the vacuum is probably picking up remnants of the soap when you are cleaning, and it is working its way into the water supply of the vacuum. This will continue to happen until you have completely removed the soap from your carpet -- and if you haven't cleaned out your vacuum very well. Try rinsing out the hoses and water tank really well, to make sure that the soap is not stuck in the vacuum itself and give it a try. Hopefully just rinsing out the machine will fix the problem.

I NEVER use more than 1/2 of the recommended amount of the cleaning solution. I read this years ago and have found it to be true. If you use the whole amount it tends to leave more residue which attracts dirt in the long run. If you have a dirty spot then pretreat it and then clean.
I often use SprayNWash to pretreat. It works great and I have it already.
I wouldn't use any oil-based cleaner such as pinesol, murphys oil soap or one of those to slean carpet.
Bleach will take the color out of most carpets except berber. Try it in an inconspicuous place IF you have berber. I have used it on a light colored plush in very small quantities.
The trick is:don't saturate your carpets, stay off them until completely dry, and vacuum after cleaning to pick up dried cleaner. You do not want to get your pad wet!
Good luck

this would be the soap/ water valve. it is stuck closed or isn't opened.( no cure for an non-opened valve, just replace.)