A long time ago my Profitec Pro 700 had a small leak and a puddle formed on top of my brew boiler. After repeated evaporations and the puddle being constantly replenished, this formed a mineral crust that I wanted to scrub when I noticed the problem.

The crust was worst around the safety thermostat and in my naivete I tried to removed them (by unscrewing them). However, they were seized and the stem snapped off inside the threads made for this purpose in the brew boiler.

At the time the whole machine was still under warranty so I sent it to get fixed by IDC in Canada. They basically just re-glued the thermostat in place, using an unknown, pink, soft substance that may or may not be silicone.

Now I'm servicing the boiler and during the various manipulation the thermostats came off. I cleaned them and now have to re-glue them on the boiler. I know I should use a very small drop of thermal paste between the thermostat and the boiler itself; but what would you use to fix them in place?

One possibility would be high-temperature thread sealant, which I think would be enough to hold the thermostats in place. Another possibility would be a threadlocker compound, but the ones I have access to have a lower (albeit probably sufficient) temperature range -- up to 300 F whereas the high-temperature sealant is good up to 650 F.

Any other better option for an adhesive that is heat-resistant and which would allow me to relatively easily change the parts if needed in the future?

Pic of the situation:



As always, thanks in advance for any hints / opinion / advice.

The best repair, IMO, would have been to drill out the broken stud and install new thermostats using thermal grease (paste). The repair you got was likely done using thermal adhesive (glue). Obviously, this isn't as permanent a fix as re-tapping the hole and putting in new thermostats, but it is a legitimate means to install electronic devices that lack a mechanical attachment. The trick with thermal adhesive is to press really hard on the component to ensure that only a very thin layer of adhesive remains between the thermostat and the boiler. This is for two reasons. First, the thinner the layer, the better the conductivity. Second, the strength of the bond is impaired if the adhesive is too thick, as it sets a bit soft. Another way to do it is thermal conductive adhesive tape. Finally, there are different grades of thermal adhesive. Most of the ones we see on sites such as Amazon are cheap Chinese imports; they often bond for only a few years, then give up the ghost. However, if you shop around, you can find thermal adhesive at places that specialize in electronics manufacturing components. One such place is DigiKey https://www.digikey.ca/

Hey thanks for this Nunas.

Re-tapping the hole would have been difficult I think because 1) it's really small and 2) there is part of the thermostat stem in it. It's too small to use drilling techniques to get the stem out (and it's badly seized anyway), and just re-tapping the hole with the exact same size would have been prone to mis-alignment issues, etc.

The ideal way to do it I guess would have been to drill a bigger hole, fill it with a piece of metal (with a thermal adhesive I guess) and re-tap this new piece of metal. But at the end of the day, the goal here is to have a working thermostat attached to the surface of the boiler, and risking damaging the boiler in the process would have been much more expensive to repair.

Anyways, I'll look at thermal adhesives -- I guess they do the same job as an adhesive and the thermal paste. If anybody has a specific suggestion as for a good product in this category, I'm interested.

There are many thread repair kits available. Basically you drill the broken stub out with an oversized bit and then tap the hole to accept a threaded insert. Not expensive or difficult to do and much better than glue!

I've had good luck drilling out those broken bolts/ studs with a left hand drill bit. Also it's an easy fix at a good metal working shop.
D.

The broken piece of the stud should come out with a small screw extractor. I like the tapered square ones, as opposed to the ones with the backwards screw threads. You drill a little hole, then hammer the extractor in. The action of hammering in the extractor should loosen the broken stud, making it easy to back out. Or, you can drill it out. The broken stud is likely a soft metal, like brass. The boiler is really hard, stainless. It's not difficult to drill the brass with a tiny bit; you'll know right away when you hit the end, as stainless is very hard to drill. Then move up a size and drill again. Do this carefully until you think you're just to the threads on the boiler. Then, use a tap matching the size of the thread on the boiler/thermostat. Very carefully, "chase" the threads on the boiler. Much of the brass should come out fairly easily. You won't get it all out this way, as taps are tapered, but once you've gone as far as you can, you should be able to pick out any remaining pieces with a sharp awl, as the blind hole in the boiler is fairly shallow. The goal is to get back to the original stainless threads in the boiler with as little damage to them as possible (you may do some harm, but no big deal). If you do this, then put a daub of thermal grease on the thermostat and run it in; do not overtighten. But, if either of the above repairs is beyond your DIY skills, then get a good quality thermal adhesive and glue the thermostat back on. Be sure to let it set for at least a day before using, as thermal adhesive I've used takes a while to set up. 24-hours would be the minimum, but check the specs for the product you use. Thermal adhesive is often used to secure electronic devices to heat sinks. It can stand quite a bit of heat once it's set.

daviddecristoforo wrote:There are many thread repair kits available. Basically you drill the broken stub out with an oversized bit and then tap the hole to accept a threaded insert. Not expensive or difficult to do and much better than glue!

I'd try to avoid drilling into the boiler itself as the consequences of failure are much more dire than with an adhesive.

Davi-L wrote:I've had good luck drilling out those broken bolts/ studs with a left hand drill bit. Also it's an easy fix at a good metal working shop.
D.

I've never seen extractor bits this small though (seems to be 3 or 4 mm, not sure of the exact size of the hole/threads). I'm sure a metal shop could do this but I'm trying to DIY this before Christmas

Nunas wrote:Or, you can drill it out.

This is probably the way to go for a more definitive fix; I may even try it to see what it does. But I'd have to order new thermostats, so if I want flat whites on Christmas morning I'll have to go with what I can find in terms of adhesives at Canadian Tire or other hardware stores.

Thanks all for your suggestions!

Nunas wrote: Then, use a tap matching the size of the thread on the boiler/thermostat.

The tap will need to be a bottoming type [ top in the image ] as a standard tap will barely get any thread in the hole




If you've got a Dremel or similar tool, you can make a thread chaser from a stainless bolt of the same size. Cut the end dead square and then cut some vertical flutes ala a tap. The flutes need to be deep enough to catch the broken brass. Go slow and back out the chaser very frequently so as not to jam the tool.

Some high temperature grease during installation will keep water and thus corrosion out of the threads.

For the record, it seems that the standard threads on these thermostats are M4.

I'll likely use thermal paste + loctite for now and try to have lattes on Christmas morning if at all possible, but I'll sure try to properly repair this with new thermostats afterwards.

So, would you chase the existing threads with an M4 tap bit, or would you rather make a new hole altogether? Of note: I don't have a press drill, so perhaps trying to chase the existing threads would be safer.

The boiler tops are likely made on a CNC before welding.
The boiler is stainless. Not fun to drill. Or tap. M4 is pretty small and the depth is small.

Chase the brass out of the old threads.
Might not hurt to put a drop or two of vinegar in the hole a couple of times to dissolve any scale.