Stovax Riva Repair

[Dcal]

I've a Stovax Riva cassette stove that's built in to a wall.
It's in a room that doesn't get used all the time so hasn't had a huge amount of burning but it must be over 10years old.
It's been great and gives little trouble, I get the chimney cleaned once a year and the only maintenance it has had is a couple of sets of home made baffles.

Towards the end of last winter I knew it needed baffles but I didn't get around to changing them, we just kept using it.
I had been meaning to sort this all year and with the winter really starting to hit and after seeing a post by @Shox Dr on the same stove, I decided I couldn't put it off any longer. Also SWMBO was rightly getting a bit fed up with not having a working stove in the room.

I've plenty of other things to be getting on with so this has been a bit piece meal and I've just worked at it when the weathers been too bad to work outside.

Enough of the preamble
I didn't think this would be so involved so I didn't take any photos before I started, but this is the sad state of it after I started to take it apart.

Door off and fire bricks out.

Baffles had certainly seen better days but the top of the stove where the flue enters the chimney was also totally burnt out, as was the start of the flue liner.



Whats left of the fire brick





I thought about removing it to replace (or repair) it but decided to see if I could fix it in place.

To try and reduce the amount of dirt and dust escaping I fixed some Terram geofabric to the chimney breast with sash clamps.



I was then able to remove the flue pipe and cut out the top of the stove that had been burnt out with a 4 inch grinder.



I have an off cut of 5mm thick 316L stainless so decided to use this for the repair, as stainless lasts far longer than mild steel in contact with flames.

I used my Rtec plasma to rough out the replacement parts.



And welded them together with 2.5mm Bohler 316L arc welding rods.

 

[scottmk1]

Looks good so far and a good idea with the tent to allow you to repair in situ.

 

[Dcal]

Repair section finished for the top of the firebox made and m8 nuts welded for the flue outlet pipe.

Flue outlet.
I kept the original 6 inch outlet pipe section as I didn't have any suitable stainless and it wasn't totally flubbered. (pretty close though)

In hindsight I should have cut and replaced the complete top of the fire box but i didn't think it was so thin.

The plan was to install the repair plate above the original fire box top plate.
I was able to do this, but the section towards the door was very thin and I cut it too short, so it was in effect a butt and I burnt it in holes when I tried to weld it.
Also the top plate was very distorted so i used a "Porta Power" to straighten it and close the gaps.

As @zeppelin builder said in another thread, positional stainless welding isn't easy for the diyer and that's what I found when trying to weld this upside down with my head in the fire box.
It went ok until i tried to weld the section nearest the door and that was just a disaster.

In my defense I was trying to butt weld 2mm totally oxidised mild steel to 5mm stainless overhead so it was never going to be pretty and what I should have done, was cut my losses and started again, but I persevered and got it patched up (after a fashion)
I was also using 2.5mm 316L rods, but I wasn't going to waste 309s on this (even if I had them)

Next job was the baffles.

What was left of the baffles didn't give much of a pattern, so I got an installation manual off the net and used that to guess the shape and size of the baffles.



Made a template out of light steel and used that to confirm sizes.

 

[Dcal]

The last couple of sets of baffles I installed were made from mild steel and didn't last that long.
This time I decided to use 5mm 316L stainless, reckoning they should last a good bit longer.

I cut the rough sizes I needed with the plasma and cut to final size with the 9 inch grinder.
The plan was to then cut part way through the plates where I needed a fold and bend them on my folder.

Even with only 1mm of steel left uncut, the folder didn't want to play ball, the sheets were too thick to clamp properly and I was going to brake it if I persevered.
A new plan was required so I decided to make a press brake type attachment of my 50t hydraulic press.

Started out with some 10mm plate I had laying about, sharpened one edge to a 90 degree bevel with the grinder, cut it in two, then welded them together with 7018s to form a T.
In hindsight cutting the plate in half wasn't the right thing to do.
I should have kept the blade of the brake (the bit sharpened to the bevel) the full size as it would have spread the point load from the ram into the plate better, but that would have used twice as muck steel and I'm a miserable git.
Of course the blade bent in use, this isn't surprising, as it took 8 ton to form the bend! (If the gauge on my press is to be believed)

Next I welded some 50 x 50 angle to a base plate and stiffened it up with a few gussets.

With this rough and ready tool I was able to bend the plates to the required shapes but I still needed to part cut through the bend locations with a slitting disk.
This part cut had the added benefit of making the setup for the folds much easier.

When all the bends were formed, I welded the open cuts with 316L stick welding rods.

I used Bohler 2.5 rods that are donkeys old but they worked well enough for the purpose, just a few pin holes to complain about.
The welding warped the steel but I was able to straighten them in the press.

Finished baffles

 

[gaz1]

been watching since you posted this up

looking really good on the plates and your welds

though id have upgraded the top plate all the way across inside of it and welded just the sides the top plate catches all the heat

your new plates look good but 5mm is not good to bend in a vice it can be done though as ive done it often but my vice was on the floor

good repair on it so far

 

[Shox Dr]

Brave man.

Thankfully as mine is free standing I cut the whole top out. Make sure the upper baffle has a good fit to the roof. Otherwise hot gases can squeeze past, burning the roof out again. I did think about extending it to the very front to protect the roof, but In the end I didnt bother

 

[Dcal]

Thanks for the advice lads.
It's too late now to start fixing the complete roof of the stove but if I was doing something similar again I would certainly replace the whole thing.
Thinking about what you have said and getting a better understanding of how the stove is designed, I will install a thin piece of stainless between the top baffle and the front of the stove to seal and protect the area. If / when it burns out it will be easy to replace, so worth a try.

Next job was the fire bricks.
The fire bricks can be bought from Stovax, but instead of paying up and waiting for them to arrive. I bought a small sheet of 25mm thick board and cut my own.

Cuts easily with a hand saw but I discovered the ideal tool to do the final shaping and filing to size was one of the Farriers rasps that I got from @hotponyshoes many moons ago.

There are 11 fire bricks and most of them have cutouts or bevels and the rasp was perfect for the job.

Before I installed the brick for the final time I gave the metal bits a tidy up.
The inbuilt bits I cleaned up with a sander and needle gun

Then masked up and a few coats of black VHT paint

The bits that I could remove, I grit blasted in my cabinet and painted in the garage.

 

[gaz1]

nice job of the stove

just a note here put your plate over the lip at the front underneath your first bolt on plate that will hold it in place

if you look at your pic before welding flue pipe you will understand what i mean

that piece can be curved or angled it wont any difference its only a deflector plate

 

[Dcal]

nice job of the stove

just a note here put your plate over the lip at the front underneath your first bolt on plate that will hold it in place

if you look at your pic before welding flue pipe you will understand what i mean

that piece can be curved or angled it wont any difference its only a deflector plate

Thanks I'll give that a try.

 

[Dcal]

Almost done, just putting it back together again.

I cleaned the glass as well as I could.
It is far from perfect but will do for now.
When removing the stainless slips that hold the glass in place, a couple of the m4 countersunk set screws didn't want to come out.

Built up a blob of stainless on the set screw, then welded a M5 nut to the blob and was able to unscrew them.

Next job was to make stainless slips to hold the fire brick in place (while allowing the bottom baffle to be installed) and pop riveted to the secondary air inlet pipes. They were originally fixed with set screws but I had to drill them all out, so stainless rivets seemed a better option.

The holes without rivets are for the secondary air supply.

Final job is to make and install a heat shield as @gaz1 has suggested then then it's ready for a test burn.

 

[Dcal]

Final job is the additional heat shield made and fitted under the top baffle and the lip of the glass air wash.
Used some 1mm 316 I had laying around.

First fire set and a low burn to give everything a chance to dry and cure.
Think I can call it done.

Thanks all for the help and interest

 

[awemawson]

Very nice reconstruction sir, I take my hat off to you

Can you please give details of the 25 mm insulation / fire board that you used - it looks very useful stuff for a variety of applications.

 

[gaz1]

nice recondition of the stove spot on there

its only a deflector of hot air

but with stove being so thin it was advisable to use it

just keep an eye on the secondary air plates for warping and changing the secondary air input into the stove and that deflector plate stainless steel

 

[Dcal]

Very nice reconstruction sir, I take my hat off to you

Can you please give details of the 25 mm insulation / fire board that you used - it looks very useful stuff for a variety of applications.

It's vermiculite fire board I think, nothing special.
I got it from a local stove shop.

If it's anything like the stuff that came in the stove it can take some heat. Some of the bricks were cracked but they were all present and doing their job after 10 years

 

[gaz1]

just a reminder here have you done service checks on your stove since you repaired the stove

if not i think you should do so and this should have been yearly or every 6 months

 

[Dcal]

Cleaned the chimney at the start of last year's burning season and checked it out, seems to be holding up well.
Will do the same this year.

 

[gaz1]

hows your bolts and plates looking and holding up with the heat of the fire

have you checked and replaced where needed or are you just hopping they come back out when repairs are needed