Unvented DHQ layout question

We have a recently installed unvented DHW system installed in an inherited bungalow that we will soon be moving into. That system has two expansion vessels, one for the CH and one for the DHW. OK, so far so good, I get that. But does that mean that the incoming cold water mains supply is also connected indirectly to the DHW expansion vessel, via the DHW tank, albeit through a pressure reducer?
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Chris

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More or less, yes. I believe it’s normally T’ed off the “cold side” (before the tank) but after the pressure regulating valve.
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Tim
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Thanks, that's more or less what I suspected. I asked because the bungalow layout has two outside taps, one at the front, the other at the back. The one at the front was a replacement for an original, and being a replacement, also had to have a check valve added to the pipework, which got nackered in the recent cold snap. But the one at the back is at the end of a run of pipe that didn't get replaced and has no check valve. I had remembered to turn off the water but forgot I should also have drained it. Cold weather such as that is rare down here. I just wondered what would happen if that tap froze and the ice migrated back along the pipe a short way, thereby raising the pressure in the rest of the pipework. I presume the expansion vessel would have taken up the increase in pressure to some extent.
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Chris

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I guess for a few quid you could try it with one of those pipe freezing kits that you see around for silly high prices. Brian
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