Immersion heater blank

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Hello I have an RM stainless hot water cylinder installed in 2013. The immersion heater brass blanking plug has corroded through and started to leak.

I measured the plug and it’s about 2 1/4” across and saw that Screwfix do a 2 1/4” blank plug, but it is too big for my cylinder.

here’s a couple of pictures of my plug. Can anyone advise what size I need, and where I might be able to get one reasonably quickly?

ACF63155-CC22-48C3-8199-121696B2638D.jpeg
E4962915-DF37-47FB-B813-22C35DF14C9B.jpeg
E6BBDEA3-0AF5-4DDC-AE88-1853C1D0D0F5.jpeg
 
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Is it leaking around the edge? If so wrap some ptfe tape around the thread, (clockwise) and screw it back in again.

Andy
 
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ask R M direct on 0800 218 2 218 screwfix et al. supply standard size plugs - never seen another size for immersions.
 
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Is it leaking around the edge? If so wrap some ptfe tape around the thread, (clockwise) and screw it back in again.

Andy

I’m not sure to be honest but I’m reluctant to re-use it due to the amount of corrosion it’s showing on both sides.

Any idea what would have caused it to corrode like this?
 
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Any idea what would have caused it to corrode like this?

Yes. Voltaic corrosion caused by disimilar metals connected by an electrolyte, though from your photos it looks more like it has a coating of limescale rather than corroded. I take it that your cylinder is of the vented type. Best speak to RM, but your measurements indicate the plug size is 1 3/4"bsp, the size determined by the nominal bore of the pipe that would have that thread size cut into its outer diameter.
IIRC RM don't supply plugs with their vented S/S cylinders, so this faux pas may belong to the installer.

MM
 
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is it a vented or unvented cylinder ? some unvented cylinders the thread for immersions is different to stop the wrong immersion being fitted
 
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Thanks. I’m in Yorkshire and we don’t really have any problems with limescale here so dissimilar metals sounds likely. The rest of the cylinder is spotless inside. It’s an unvented cylinder.
 
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Not to be a stickler but as it's an unvented then is it a qualified engineer that's performing the work? The reason I ask is that it's a key element of working with a SS unvented cylinder that mixing metals will cause corrosion issues.

I would be really surprised that RM would supply their SS steel cylinder just with a brass blank, all their cylinders would ship with the correct Incoloy immersion elements. Depending on the type of SS then the Brass would always corrode to the SS, hence why the elements are incoloy, so as to resist that reaction.
 
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Hello I have an RM stainless hot water cylinder installed in 2013. The immersion heater brass blanking plug has corroded through and started to leak.

I measured the plug and it’s about 2 1/4” across and saw that Screwfix do a 2 1/4” blank plug, but it is too big for my cylinder.

here’s a couple of pictures of my plug. Can anyone advise what size I need, and where I might be able to get one reasonably quickly?

View attachment 269400 View attachment 269401 View attachment 269402
Immersion heaters are 2-1/4" BSP, but that's nominal diameter. The actual diameter across the outside of the thread is about 67.6mm, 2.7in. My data doesn't show 2-1/4", but that's the average of 2" and 2-1/2"
 
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Not to be a stickler but as it's an unvented then is it a qualified engineer that's performing the work? The reason I ask is that it's a key element of working with a SS unvented cylinder that mixing metals will cause corrosion issues.

I would be really surprised that RM would supply their SS steel cylinder just with a brass blank, all their cylinders would ship with the correct Incoloy immersion elements. Depending on the type of SS then the Brass would always corrode to the SS, hence why the elements are incoloy, so as to resist that reaction.

I’m assuming it was installed by a qualified person as it’s original to the house which was built in 2013
 
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I’m assuming it was installed by a qualified person as it’s original to the house which was built in 2013
Should be marked on the benchmark in the MI. It should also have been notified so a LABC cert should have been issued too.

Might be an idea to contact RM and see if they would have shipped with a brass blank, they may be able to suggest an alternative or just fit a proper incoloy element. I wouldn't replace it with another brass blank though as it will eventually just eat that one too, not really what would be recommend for a pressurised cylinder.
 
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Yeah I’ll give RM a call and see what they suggest.

Just out of curiosity would the same occur with PRVs as all the unvented stainless cylinders I wire up appear to have brass PRVs or are they actually made of a different material?
 
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That is an excellent question, I can only surmise that the TPRV may be in a non SS tapping or there is material/tape that separates the brass from the SS or the valves are actually a different material . Next question would then be, why wouldn't the immersion tapping be the same , guess that's the reason they are made of incaloy.

Would be interesting to hear what RM have to say.
 

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