On Mon, 21 Jan 2013 13:56:19 +0000, Gypsygirl
wrote:


I have a 12year old potterton suprima . It has been a good faithful
boiler until 3 years ago when the radiators just stopped getting hot
(warm it could manage ) and 2 radiators bairly that . System was flushed
last year and pump is new . Can it be because there is no pump over run,
boiler kicks on runs for about 2 mins then shuts off from wall
thermostat ,water out and water returning red hot (boiler clonks and
ticks) but radiators only warm ?
Am now fixated that the pump should run the hot water around the system
for longer ie adding pipe stat or remote timer but started to read blogs
that say pump over run simply dumps the heat and will not circulate it
round the radiators once the boiler is off ?

Apologies if this is all a bit vague but trying just to post essentials
if anyone is kind enough to respond can add any details required .

Hot water systems I have had work like this. There are two main
controls (plus some safeties). the wall thermostat and the boiler
temp. control.

When the wall thermostat calls for heat, the circulator runs and the
boiler temp control is enabled.

If the water is below the min temp set on the controller, the burner
will fire and will continue to fire until 1)the wall thermostat is
satisfied or 2) the water temperature high limit is reached.

So say it's really cold in the house because the thermostat was turned
down and now you turn it up. What usually happens is the circulator
pump begins to run and the burner fires because the water is cool.
Everything continues to run until the water temp hits max. Then the
burner shuts off but the circulator continues running. Eventually,
the water will fall below the low temp limit and the burner will fire
again.

Eventually, the wall thermostat is satisfied because the house warmed
up and the circulator and burner shut off.

There are lots of variations of this. Some systems have multiple
zones, which can have multiple circulators, or one circ with zone
valves. Multiple zones will have multiple thermostats.

Or you can have valves on individual radiators, with a main loop for
the water with branch tees to the radiators.

Some systems keep the water temp in operating range even if the wall
thermostat isn't calling for heat, but this is rare on newer systems.


From your description, it sounds like the controls might be wired
wrong and the circulator is being stopped when the water reaches upper
limit. This is not only wrong, but is a potential safety issue.

You may want to try to find a tech who really understands HWH systems
and boilers to figure out why it's so messed up.

Another point. You can have an air locked system and still not be
able to get air out of any radiators. In this case system usually has
be power purged. This can happen with funky piping runs or pipes that
have sagged over time.

Good Luck,

Paul F.