Truma Cascade immersion - PRV replacement

Just replaced the Truma Cascade Immersion heater pressure relief valve on the Clubman. As suspected, after 21 years, it wasn't keen on coming out. It started to unscrew but then sheared leaving the threaded bit in the heater. It took a while but by using a small file and hacksaw blade to create a screwdriver slot in it (without damaging the thread) and gently hammering a large screwdriver in, I managed to unscrew the broken end.
Then I used a vacuum cleaner and small brush to remove the swarf.
Then I cut a groove in a bolt and gradually ran that down the hole to clean out the thread.
I didn't want to put any grease or anything on the thread as I didn't want it getting in the water.

Hope this helps anyone trying to do the same job  

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I did that job about 8 years ago on our Symphony. As you say the important thing is not to damage the thread. I tried the large screwdriver like you but it wouldn't budge so I did it by drilling the broken piece left in , increasing size of drill a little at a time until the last bits fell out before hitting the thread.

Amazing job! Well done. Keeping swarf out of the heater must have been a huge challenge! How much does a new heater cost?

Well done from a retired gas boiler engineer. I am properly impressed. And showing the invoice from Truma was very encouraging, that they don't overcharge for parts. At least, not that part anyway! A bit worrying though that it should seize, I have never had that trouble on domestic gas boilers. You don't say what the two metals were, presumably they are incompatible?
Worried now that mine might seize. . . . . .

Don't panic gassy, we are talking about Cascade water heaters here (taken over by Truma way back in 1999, that's why the packaging is from Truma), made by Carver. The pressure valve is made of a  nylon/polythene inserted into an aluminium frame.

Here's the offending item 

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gassygassy wrote:Well done from a retired gas boiler engineer. I am properly impressed. And showing the invoice from Truma was very encouraging, that they don't overcharge for parts. At least, not that part anyway! A bit worrying though that it should seize, I have never had that trouble on domestic gas boilers. You don't say what the two metals were, presumably they are incompatible?
Worried now that mine might seize. . . . . .

I replaced it because the screwdriver slot had broken. I guess the plastic hardens up over 21 years. It was still possible to operate it by taking the cover off but with the replacement valve costing less than £10, my OCD won out .

On my 21st year of mono ownership.  All the Cascade water connections are plastic and harden with age. Best practice is to renew every five years.  As described drilling out until the bits fall apart works.  The parts appear to be disapearing from dealer shelves. Mine are due . The critical one is the one way valve that keeps heated water in the boiler.  Its likely  the threads are standard plumbing sizes and  similar items  might be found at a plumbers merchants. I have  one in my bits box and will see if I can identify the thread.

Next challenge: Giving the plastic cover a coat of paint while it's off. Anyone got experience of this? According to the internet I need a 'Adhesion promoter', some paint and some lacquer.

Yes - I did mine with just Hycote plastic primer and ordinary rattle-can cellulose (or whatever substitutes for that in the solvent-based paints these days), colour-matched to the rest of the van.

I was very sceptical and expected it to bubble off the first time the Cascade lit up! But it didn't, and it looked as good when I sold the van 2 years later. I should add though that mine looked (and physically was) quite rough before the spraying, so adhesion of the paint was very good.

I worked a lot with plastics, & as Roopert stated above, a plastic primer is required before paint as it slightly dissolves/melts the surface leaving a good substrate for paint adhesion, failure to do so & there's a good chance that your new paint will flake off. It will DRY, but not stick!!

I think you'll find the cascade ' cover' is the vent which is cast aluminium.

Paul - maybe this has varied with time, but I know that the Cascade (2?) on my 1999 conversion had an outer cover that was made of some form of fibre-filled plastic. I know a bit about its internal makeup because one of my lovely neighbours backed her car into it, breaking it, and drove away without telling me. I repaired it successfully with Araldite, and sprayed it a few years later.

Roopert wrote:Paul - maybe this has varied with time, but I know that the Cascade (2?) on my 1999 conversion had an outer cover that was made of some form of fibre-filled plastic. I know a bit about its internal makeup because one of my lovely neighbours backed her car into it, breaking it, and drove away without telling me. I repaired it successfully with Araldite, and sprayed it a few years later.

I have one in the garage which I'm sure is cast aluminium but you could well be right. Whatever they are made of, they are extremely fragile and go brittle with age.

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This is it. It's pretty manky so not difficult to improve. The surface is pretty rough. I think from the texture of the inside it was quite smooth when new. I think the rough texture should help with adhesion but I would like to make sure with an 'adhesion promoter'. I'll see if I can find some Hycote. The structure underneath this cover looks to be cast aluminium. Maybe there was a misunderstanding somewhere.

That's pretty much what mine looked like. I think the top (smooth) surface degrades in UV light and drops off, leaving a sort of fibrous finish which is very difficult to clean. I only used Hycote as that was the make that happened to be available - I suspect that any plastic primer will probably be Ok.

IIRC, this is where I bought it - lots cheaper than Halfords, even with shipping included!

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This is it after two coats of 'Hycote' plastic primer and 3 coats of the local hardware store's gloss white cellulose. The paint thickness is starting to soften the definition of the logo at this point. The Hycote does recommend using an 'adhesion promoter' so we will see how it stands up to use this summer. A four week tour of Scotland should prove test enough . I dismantled it for painting and gave the screws a coat of rust converter and WD40 for good measure. I like to be thorough.  .

It looks good - definitely worth doing. I'm a bit surprised that you have corrosion on the fixing screws, as I recall that all of mine were stainless - perhaps that's one of the things that was changed during the years of production.

Roopert wrote:It looks good - definitely worth doing. I'm a bit surprised that you have corrosion on the fixing screws, as I recall that all of mine were stainless - perhaps that's one of the things that was changed during the years of production.

I refer to the 8 long screws that hold the two parts of the cover together. I dismantled it to get good painting access to the plastic parts and avoid painting the metal parts. The four screws that hold it to the body are indeed stainless. As I say, I like to be thorough