immersion heater seal

[Gazz]

guess my last post wont be read due to the title i gave it, but i really do have a leaky wet flange.....

the immersion heater flange on the motorhomes calorifier,

old seal was a thin O ring, new seal is a waxed gasket the width of the entire flange seating area, still leaks, but not as much,

what would be the recomended sealant to use on the flange? i'll avoid boss white as i might want to take it appart sometime in the future, i could use silicone sealant, but i'd rather not if something better is recomended,

there's tru blu, which mentions it's for flange mating surfaces, and it's recomended for joints subject to vibration, which is the case in a motorhome.

or would liquid ptfe be better? i'll wrap some ptfe tape around the threads, even tho i know the seal is the flange it's self, but it seems recomended to help getting the thing undone at a later date,

Basicaly it'll have to be something i can get from toolstation, as that's where i'm going tommorow,

they do a washer that looks like it's a fiber type, would one of those be better? assuming toolstations washers are fibre??

[Dave Baker]

Had the same problem on a domestic immersion tank where the paper gasket alone simply wouldn't seal it. Maybe the flange was distorted somehow. A smear of ordinary clear silicone on both sides of the gasket sorted it. Make sure to let it cure overnight before filling with water again though.

[Tabby]

That's what I'd reach for. Get the soft stuff and its very easy to cut or break later. High modulus? I can never remember which is which.

NT

[dom]

Use Loctite 55 sealing cord:

's like a thick, heavy, waxy PTFE tape made into a cord (in fact a bit like a "heavy dental floss").

Has been recommended many times on here, and I've used it to seal an immersion heater with an 8 metre pressure head. Worked perfectly, first time.

[Dave Liquorice]

Fernox LSX. Silicone will no doubt work but how easy it will be to break the joint again later is another matter. Getting immersions out can be a barstweard of a job with just corrosion let alone an effective glue in the joint...

As the thin(?), relatively hard(?), waxed gasket hasn't sealed that suggests some distorion or damage to the flange, either or both sides. A thicker, softer, fibre washer will conform better to the distortion and thus stand more chance of sealing. Fibre washers also "selfseal" as they expand when they get wet.

[Gazz]

well, none of those suggestion will work, the damn thing was left full of water over winter, how i dont know as i drain the system down and blow the pipes thru with compressed air, could have a non return valve stuck i guess and it backfilled or something, but either way, the damn thing has expanded and cracked the solder joints.

i can see 3 or 4 cracks in the immersion heater flange solder ring, and it deffo leaks out of some of them as i scraped the insulation off around there, but the whole tank has expanded enough to crack the insulation, and the seam shows signs of external cracks,

apparantly it's a folded and silver soldered join there,

bod know if it can be fixed, the insulation will need stripping off for sure, then i guess every fitting and all seams re-soldered, and re-insulated,

it's about £350 for a new calorifier, which i can not afford anyway, so looks like im screwed good and proper.

[YAPH]

I've no idea how motorhome immersion heater fittings compare with those on domestic hot water cylinder immersion heaters, but on the latter I use a *lot* of PTFE tape wound round the thread and built up heavily onto the shoulder so that, as the heater is tightened, the PTFE adds to the fibre washer in sealing the face of the heater flange to the flange on the cylinder boss.

[Gazz]

same as a home one, it's really a boat item, very few motorhomes use the type of heating system i have fitted to mine, more usefull if you move the van every day, as you heat the water for free using the waste engine heat,

it's basicaly a mini hot water cylinder, but an unvented one, however it seems the copper it a lot thicker than a domestic cylinder, to take the stresses of being full of water and in a moving vehicle/boat at the same time as being heated to 85 to 90 degrees C.

But alas the sealing surface wasnt the cause of the leak, a wrap of ptfe tape around the threads, a new fibre washer and some tru blu sealant (which seems very much like blue hylomar used on engines) and i had the heater to flange sealed nicely,

then i was able to find the true source of the leak, cylinder had been left full of water over winter, frozen, bulged, and cracked the apparantly silver soldered joins,

as it's a pressure vessle i cant get it repaired and re-certified, so need a new un, nice start to the season,