Anything that holds up well at high temperature. And easy to remove.

It seems that permabond A131 is a good fit used by some manufacturers but they are hard to get.

I've used loctite 542 but they adds to the difficulty to removing.

Also any problem with using an impact wrench to remove? Will there be any risk of damage? I will still hand tighten by hand to have better control and reduce the risk.

Hi Flitzgordon Great question and one that many consider.

*EDIT: cafeIKE has wisely mentioned below that not all threadlockers and sealants are food/water safe . . . there is no substitution for experience! See my post below his for some clarification. I've edited this post to strike out the text discussing use of a certain low strength threadlocker that is not food/water safe and will send the text to Flitzgordon directly in a PM as well. While some threadlockers/sealants may indicate that are safe for use around food equipment, they may not be safe for use when in direct contact with Food or Water.

Definitely LOCTITE 222 is a low strength thread locker that will provide a high quality seal but not add any extra torque force to removal at a t later time. Typcically LOCTITE (a Henkel product) is for small fittings 1/4" and screws etc. but it does form a seal anaerobically when in a metal compression joint, even on larger fittings, such as a 1" or larger Heating Element/HX fitting.

A Medium Strength Thread Locker could be used as well (like your loctite 542, but as you notice, it does require slightly increased torque to remove). Sometimes heat is required to ease removal of a medium or high strength Thread Locker.

Home-Barista site sponsor, Elektros sells and recommends Loxeal 24-18, a low strength Thread Locker but as mentioned above, LOCTITE 222 is the compatible LOCTITE product. Here's a chart showing some of the comparison, specifically for the Elektro's 24-18 and LOCTITE 222 equivalent . . .

The heating element gasket should provide all the seal required. If it doesn't, there is something wrong with the face on the element or the boiler.

Be sure to check the MSDS for any product in contact with the water.

Yes for sure cafeIKE is 100% correct . . . Loctite 222 is for non-food contact applications. There are a number of HENKEL products listed on the NSFⓇ website under three categories/registrations. There are some Loctite products that can be used in and around food component/thread sealing applications but Loctite 222 is not one of them. Its ok to use on screws, and threads that do no not come in contact with water or food. (I've edited the above post picture to clarify that Loctite 222 is for non-food/water thread applications).

Here is a link to the "NSFⓇ" organization that has a search feature to check on whether a threadlocker is safe to use in water and food applications. <<Click Here to visit NSFⓇ website>>. It should also be mentioned that these certifications, whether through the US Food and Drug Administration (FDA), Canadian Food Inspection Agency (CFIA), or other worldwide agency are constantly in motion and somewhat nebulous. Avoiding use of threadlockers may not a bad thing and a wrench can often solve a leak. Some teflon tape not a bad thing.

Stefano's Espresso Care website has several thread sealants listed, some of which are clearly identified for consumers relating to their food safety. An excellent resource where "thread sealant" can be entered in the search field to find options . . . <<Click Here to visit Stefano's Espresso Care>>

And here's a screenshot showing some LOCTITE products indicating which may be safe for use in specific types of applications (note, some of the links listed on the page may not be valid over time). . . a superb topic and one that proves that the experienced people's knowledge on Home-Barista is priceless and invaluable!! Thanks much to cafeIKE's brilliant catch on this one that needed addressing

. . . and here's an overview of the categories . . .

. . . and here's a loctite product, 2046, that appears to be certified as food and water contact safe . . . the problem is this single tube costs nearly $400.00 . . . yep Four Hundred . . . that advice above by cafeIKE that the gasket should be enough is looking better and better every second haha!:

Several products from Loxeal on the market (we and other vendors carry)
are water potable friendly
they just didn't go through the official expensive certification,
this is a statement made to me by the owner of the company in question.