Cast iron repair advice

[angrybird]

We recently had a Biomass boiler fitted,when the cold spell was forecast we drained the whole system as we don't live in our renovation project yet.
There was about 2 inches of water left in the bottom of the boiler there is no way of removing this.On return to our remote Farmhouse the system was refilled only to find was a 6 inch split in the cast iron!
Does anyone have any advice on what could be used to 'seal/repair the split please. There is a possibility of removing the boiler and replacing the back panel where the split is but it is going to be a huge job

Second part of my cast iron dilemma. I want to keep the high level toilet cistern, I have removed many layers of paint but now there is a tiny pin hole just above the lettering ,this is causing a very small leak but as I want to respray the cistern I'm looking for a product to seal the hole any ideas much appreciated

*The picture is of the cistern covered in paint stripper not end result.


Jacqueline x

 

[Me!]

The cistern can be fixed with any one of a number of two-pack epoxy type products. Araldite, JB Weld, Isopon P38, take your pick.
Just make sure the iron is nice and clean and dry, then mix up the epoxy and force some into the hole from the inside of the cistern. Then wait for the required number of hours for it to harden before painting.

For the boiler however, that doesn't sound so easy. Is this a bit of cast iron that has flames on one side of it and water on the other?
There is a process called metal stitching that is used on cast iron, but is it quite a specialist process so I've only ever seen it used on something that is irreplaceable. Probably because if something is replaceable then that is likely to be a cheaper option than metal stitching it.

 

[MikeG]

I wouldn't think you've any chance with the boiler, I'm afraid. I certainly wouldn't want to risk a repaired plate inside a boiler of mine. Replacing either the plate, or the whole boiler, looks favourite to me.

 

[Flyfisher]

Unlucky to have the boiler split by a couple of inches of water freezing - I'd have expected the ice to have expanded upwards into the empty space rather build up enough pressure to split cast iron.

Cast iron can be welded but it's a bit of a specialised job and usually involves carefully heating and cooling the entire piece so as to avoid high thermal gradients and even more cracking. Might be worth talking to the boiler supplier but I'd bet a replacement part would cost less than a repair in this case . . . though I appreciate 'less' will still involve a fair sum.

I'm confident you'll have more luck with the cistern, especially with the pinhole being so high up the side so there will be very little water pressure involved. I'd go with Me!'s suggestions of something epoxy-like. Should be fine.

 

[angrybird]

Hi me! Thank you for your reply
It's the outer leaf on the boiler, there is no flame touching this part only hot water.
We have been to see a farrier he recommended grinding out a 3mm V groove down the centre of the split and then small stitch grooves horizontally across,then to apply epoxy to fill the split and grooves then a layer of fibre glass mesh followed by another layer of epoxy then leave it to cure for 12 hours
I don't know if this is a waste of time but thought it was worth a try before having to take the boiler to pieces
Jacqueline x

 

[angrybird]

Unlucky to have the boiler split by a couple of inches of water freezing - I'd have expected the ice to have expanded upwards into the empty space rather build up enough pressure to split cast iron.

Cast iron can be welded but it's a bit of a specialised job and usually involves carefully heating and cooling the entire piece so as to avoid high thermal gradients and even more cracking. Might be worth talking to the boiler supplier but I'd bet a replacement part would cost less than a repair in this case . . . though I appreciate 'less' will still involve a fair sum.

I'm confident you'll have more luck with the cistern, especially with the pinhole being so high up the side so there will be very little water pressure involved. I'd go with Me!'s suggestions of something epoxy-like. Should be fine.

Thank you for your reply
We are wondering now if there has always been a split in the cast as the underfloor heating has always been loosing pressure.maybe the frozen water caused the cast to split further?

 

[angrybird]

I wouldn't think you've any chance with the boiler, I'm afraid. I certainly wouldn't want to risk a repaired plate inside a boiler of mine. Replacing either the plate, or the whole boiler, looks favourite to me.

Not really what I wanted to hear as the boiler is less than 6 months old we are trying the Farriers suggestion of the epoxy but it's looking more like dismantling the boiler and replacing the plate

 

[Easrow]

If it's only 6 months old surely it's under some sort of warranty so could take it back.

 

[Me!]

Hi me! Thank you for your reply
It's the outer leaf on the boiler, there is no flame touching this part only hot water.
We have been to see a farrier he recommended grinding out a 3mm V groove down the centre of the split and then small stitch grooves horizontally across,then to apply epoxy to fill the split and grooves then a layer of fibre glass mesh followed by another layer of epoxy then leave it to cure for 12 hours
I don't know if this is a waste of time but thought it was worth a try before having to take the boiler to pieces
Jacqueline x

Well, if you are going to give it a try, then it is very important that you get the ends of the split nicely smooth and round to prevent it spreading further. You can do this by drilling holes at either end and then filing or reaming them smooth. Smooth and round is the key thing you are trying to achieve here as this helps prevent a new split forming. Then after cutting the grooves as suggested by your farrier I'd grind or power-sand all the surrounding area clean to ensure maximum adhesion of the epoxy. And personally, the epoxy I'd use here is a very specific one called Isopon P40. Unlike the three I mentioned earlier, P40 is a resin that contains lengths of glass fibre already mixed up in it, so this gives it a lot more strength than just plain resin when used bridging gaps. If you've never used it before, then try it out on a dummy job first as it is quite strange stuff to handle and control if you have never done it before. And remember you've only got about 5 minutes to use it before it starts to go hard, so don't mix up too much at once.

Good luck, and now you've said this only gets to hot water temperature rather than flame temperature, I'm fairly confident that the repair will work at least in the short term. However, I'm not confident that it will last for the lifetime of a boiler, so be prepared for another water leak in the future.

 

[bobby spray]

you can also braze cast iron, stronger than expoxy but weaker than welding - but a good deal easier.

 

[88v8]

We are wondering now if there has always been a split in the cast as the underfloor heating has always been losing pressure.

Pressure?
Repairing the crack so it will hold water is one thing, repairing it to resist pressure is quite another. Is this a pressurised system?

Leaving that aside, the problem here is temperature cycling. That will really stress the repair and after a few weeks it may start to leak again.

I would favour brazing, but not sure it will last unless the whole plate is heated, and I mean seriously heated so it's glowing red hot, while it's being brazed. Then it needs to be cooled very slowly by burying it in sand otherwise as FF says, it will develop more cracks. So repair in-situ, hmmm.
There's also the question of the remaining guarantee and what the manufacturers might say about a repair.

For the future, you might add some of this to your normal system inhibitor.
https://www.sentinelprotects.com/uk/support/guides/how-to-protect-central-heating-against-freezing-temperatures

I wonder if your Household insurance may cough up? Provided you didn't leave the house empty more than 30 days. Worth a look.

Ivor