Silver solder.

Silver solder.

This topic has 5 replies, 5 voices, and was last updated 8 October 2026 at 17:27 by jon hill 3.

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8 October 2026 at 15:36 #868442
Michael Callaghan
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@michaelcallaghan68621
Hi, I need to make some repairs to a copper boiler. Given the price of solder from U.K. suppliers I had a look at other sites. However they are giving prices for 5 percent to 30 percent. I take it the lower value is low temp solder.

what do I need. Thanks
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8 October 2026 at 16:16 #868445
JasonB
Moderator
@jasonb
No, a 30% solder will have a higher melting point than 55%

The 5% probably has about 1/3rd zinc in it so not what you want for a boiler, again higher melting point than 55%
8 October 2026 at 16:45 #868453
Dave Halford
Participant
@davehalford22513
Some strip silver solders are for jewellers, also the very fine wires.

The price of silver is the driver and that’s an international price on the metals market. If you see cheap 55% it is not real unless from a show in the UK.
8 October 2026 at 16:55 #868456
Baz
Participant
@baz89810
For boiler work and any other model engineering related silver soldering you need something like Silverflo 55, the modern cadmium free equivalent to Easyflo No2. If you are going to the Midlands exhibition next week there will be a stand there where you will be able to buy what you require and get free expert advice, I would name them but don’t know if we are allowed to on this site, the chap you need to speak to will giving a talk on silver soldering.
8 October 2026 at 17:00 #868459
JasonB
Moderator
@jasonb
You don’t need 55 for all ME work, the lower silver content ones are fine for fabricated parts particularly if steel as there is no risk of it distorting due to the higher temps. Just needs a bit more heat.

But don’t take shortcuts with cheaper low silver content for boilers.

That 5% stuff is OK for refridgeration and HVAC work but not a model boiler.
8 October 2026 at 17:27 #868463
jon hill 3
Participant
@jonhill3
I know I might get hated for this however its probably a good thing that cadmium baring solder is now discontinued. My dad used a lot of it in boiler making and it could have been a contributory factor in his terminal cancer.

Out of interest could scrap 0.925 silver be used for copper soldering? For example cutting strips from scrap bought from a pawn broker / jeweller…
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