On Mon, 8 Mar 2021 22:18:28 +0000, Steve Walker
wrote:

On 08/03/2021 11:42, Davidm wrote:
On 7 Mar 2021 17:20:54 GMT, Tim+ wrote:

The cheapskate who installed out CH didn’t fit either, just a gate valve
cracked open a bit, which gets a bit noisy as the TRVs throttle back. I’m
about to fit a new pump and now seems like a good time to sort this.

Any pros and cons to any particular valves? Any recommended magnetic
filters that don’t cost an arm and a leg and are easy to fit?

Tim
I've had two Honeywell DU145 auto bypass valves fail in the last 10
years. Bloody things fail open, or partly open, so hot water is
flowing through the bypass loop even when the zone valve(s) are open.
I seem to recall reading somewhere that building (or some other) regs
mandate a bypass valve in CH systems. Can't find the reference now, so
don't know if true.
I'd thought about putting a normally open version of a zone valve in
the bypass loop, driven closed by the boiler call signal from the CH &
HW valves, so whenever there's a call for heat the bypass closes,
otherwise it stays open (including on pump overrun). Dunno if the
micro switches in the CH & HW zone valves would handle the additional
load though. (S-Plan system btw).

Easily. The microswitches are typically rated at least 5 to 6A and can
be higher depending upon make. The additional valve will take about 7W,
so an extra 30mA.

Thanks Steve!