"David Hearn" wrote in message
...
BillV wrote:
"David Hearn" wrote in message
...
We replaced our boiler in Feb (new cast iron Ideal 15kW boiler).
System is fully pumped with 2x zone valves (one for heating, one for
water). Pump is on lowest speed (in airing cupboard next to a bed,
anything higher and it makes a loud whirr which is too noisy).

Everything has been working great, the boiler is nice and quiet and
had no problems with it. Heating on 24/7 on programmer and
controlled by programmable thermostat. Water comes on twice a day,
morning and evening for about 1 hour. The problem is that now with
[SNIP]
Any ideas?
Is there any kind of a bypass for the boiler, automatic or otherwise,
when all the TRVs shut?
e.g. non-trv bathroom rad before the valves?

On the heating circuit the hall radiator (where the room thermostat is) is
non-TRV. In the bathroom the TRV is set to max (when we arrived, it was
the
only radiator with a TRV bizarrely!). So, that satisfys the bypass for
the
heating circuit. At present, even in the hot weather we've been having,
the
bathroom radiator gets hot, so I assume Max means no-thermostatic control
and fully open. No problems when running with heating only.

On the hot water circuit there is no bypass, but then there isn't a TRV so
that's not a problem. Problem occurs when running with hot water only.

The only issue I can see then is if the boiler fires whilst both valves
are
shut/jammed. The wiring is such that when the boiler is on, at least 1
valve is open, so only the jamming situation is an issue. Is it normal to
have a bypass for jammed valves situations? Incidentally, there is a 15mm
pipe (whereas rest is 22mm) with manual valve (same as balancing valve
after
HW zone valve) which bypasses both valves. I don't know what this is for
and has always been shut.

Ahh, thats a manual bypass. Tricky to setup, it should be open a bit or
replace it with an auto-bypass valve; £25 from Screwfix , item 98894.
Your bathroom rad could have acted as a bypass if it was plumbed before the
valves.
Thats how all the houses around here were piped by the developer.
The bathroom rads get hot even in summer and they work as a bypass for the
boiler.
The only people who get problems are those turn off the bathroom rad
completely or fit a TRV.
Many modern combi/system boilers have an auto-bypass built in..