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Boiler making a loud hissing noise and pump is hot, now it keeps cutting out, bosch 400 high flow

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Sounds like a stuck expansion valve, the compressor makes pressure, but it can't be released to absorb heat from the desired environment. You could go to the manufacturer's website, request a detailed diagram of your system, find the expansion valve and order a new one. Can you put it in yourself and recharge the system? Probably not, call a repairman.

Posted on Nov 07, 2008

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