Removing boiler thermostatic valve without damage

[Skylark NW]

This is a Quick, Italian, boiler installed within a boat. The thermostatic valve has failed (stuck fully open). I've bought a like-for-like replacement but I'd appreciate some advice before tackling the job.

To remove the valve without a risk of breaking the fitting out of the boiler, I assume that I should use two pairs of Stilsons opposing each other. One holding (still) the barrel nipple and the other rotating the valve body (with the connections removed).

Any other ways to do this? Is there likely to be a sealant on the threads? Any hints and tips appreciated.

Regarding sealant, should I use some to fit the new valve? Any recommendations?

Many thanks in advance.

 

[oldbuffer]

1. Your removal method is correct. Stilsons will mark the finish of the nipple and valve, so you might consider only using them for the nipple and an "F" spanner on thevalve, protecting the threads somehow.
2. There will almost certainly be sealant on the threads, which could be one of:
2a. Some form of paste like "Boss White", in conjunction with hemp.
2b. PTFE tape.
2c. Sealant cord like Loctite 55.
2d. An anaerobic liquid sealant like Loctite 577 which will have set.
3. You will need to replace the sealant. I would suggest:
3a. Paste / hemp may not be satisfactory, particularly as orientation is important.
3b. PTFE tap would be very fiddly to get orientation correct, but could probably be done.
3c. Sealing cord gives you a degree of flexibility in that the connection can be "turned back" up to 1/4 to 1/2 turn and still seal. Male threads might need to be gently roughed up.
3d. If it were me I'd use Flomasta Pipe Seal. However, this would require internal and external threads to be well cleaned of old sealant, and to be completely grease free.

 

[Skylark NW]

3d. If it were me I'd use Flomasta Pipe Seal. However, this would require internal and external threads to be well cleaned of old sealant, and to be completely grease free.

Many thanks for your response, much appreciated.
Will the application of Flomasta Pipe Seal give me the ability to tighten and orientate the new valve to the same position as the current one, per the picture?

 

[oldbuffer]

Yes. It is a liquid sealant which sets (but allows the joint to be unsealed with force). Read the instructions that come with it, but from memory:

1. It only works on metal to metal seals, not on plastic.
2. Clean the male and female threads very thoroughly.
3. Apply a ring of sealant to the male threads. Start about one thread in from the open end, and make the ring about two threads wide.
4. Screw the parts together, and wait 10 to 15 minutes.

For your application, cleaning the female threads will probably be the most difficult. Unless you have access to a 1/2" BSP thread tap I'd suggest cutting a bit of an old wire coat hanger, flatten one end with a hammer and file a point on it. Bend the sharpened end over close to the sharp bit, at right angles, to form a crude scraper. Use this to clean all the muck out of the female threads. Male threads can be cleaned up with a wire brush. Once cleaned like this, wipe over very thoroughly with methylated spirits, NOT white spirits which leaves a residue.

Loctite 577 is a similar product, but is generally much more expensive. The Flomasta Pipe Seal is Screwfix item 4373J