On 28/02/2021 15:28, Chris Hogg wrote:
On Sun, 28 Feb 2021 14:42:21 +0000, GMM wrote:

My hot water tank has stopped getting properly hot. The heating is
working fine, so it's unlikely to be a boiler issue. The pump seems OK
and the thermostat ~seems~ to be operating fine (on the basis of a click
as you turn the knob). There's no air in the circuit judging by the
bleed valve. I'm tempted to replace the thermostat, just cos I can, but
I'm not convinced that's going to achieve anything.

Any (sensible) suggestions would be appreciated.

Standard open vented indirect tank and boiler with nothing fancy like
weather compensation etc. No recent issues. DHW timer set to run when
the heating is off.

Cheers people

What sort of DHW/CH system is it?
S-plan: https://tinyurl.com/yaxejpa6 ?
or
Y-plan: https://tinyurl.com/yd69szy9 ?

If the first, the zone valve in the DHW circuit on the LHS in the
diagram may have failed, or the controller isn't sending the 'open
valve' signal correctly.

If the second, the mid-position valve may not be working properly and
be stuck in the CH position.

I've puzzled over those sort of diagrams in the past and neither fits
the situation precisely, but I suppose the S-plan is the closer (mine
splits to two separate pumps, with a valve on the heating circuit after
its pump. No valve on the DHW side apart from the thermostat-controlled
bypass)
So far as I can tell, both valves are operating correctly, as are both
pumps, which is why I'm a bit lost in terms of th mechanical side of it....