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 .
It sounds like the water is not circulating.
There are several possible reasons.
There is air in the pipework.
A valve somewhere is not properly open(ing).
The pump is not running at correct speed/is too small.
Have a look at the pump. Most are multi-speed. If so, there is a
switch on the pump which can be moved to a higher setting.
They usually just a tiny slide on the motor bit, three possible
settings is normal. It will be marked " hi" and "lo" or similar.
Turning it up may well fix the problem. As you have had a new pump,
whoever fitted it may not have set it to the correct speed.
Read my post in the thread entitled "Bleeding Hot Water Radiators -
In a house where you typically don't have zone valves, but you do have
multiple radiator loops going to different areas of the house, the
heating contractor will often put in gate valves as "balancing valves".
The purpose of these balancing valves is to prevent all the flow from
the pump from going through the shortest radiator loop, and leaving
virtually no flow through the longer radiator loops.
It could be that someone didn't know what those valves were for, and
simply opened all of them wide open, thinking that doing so would ensure
the full flow rate of water through all of the loops.
But, if someone did do that, it would result in almost all of the water
flowing through the shortest loop, providing ample heating to that area
of the house, but suddenly NO water flow, and therefore no heat, to any
of the other radiator loops. So, at least one other area of the house
could be cold even though there's nothing wrong with the boiler, or pump
or heating system.
Hi thanks to both for your advice. I do check all radiators for air and
the only place it seems to arise sometimes is in the towel rail and i
bleed that. The pump seems to be a standard size and is running on 2 as
advised to be standard setting . I have however run it at 3 for a couple
of days and there is no difference .
Nestork Not sure what a gate valve is but i do have automatic rad valves
on all radiators .Upstairs are on 3 downstairs 6 (valves are 1-6) this
makes most downstairs hotter than hand heat but nowhere near the heat of
the boiler outlet. I have checked that none of the rad valves are
malfunctioning ie locked down but the water getting there is simply luke
Could it be the pump does not circultate the hot water long enough as
the pump runs only as long as the boilers on ? Please if you have any
further options i'm just lost .
The advice about balancing valve could be right.
There are two valves on each radiator.
One of them you adjust the temperature with.
The one at the other end needs a tool to adjust it with.
The purpose of this one is to make sure the water is forced to go
round all parts of the system.
Without them (or if they were all wide open) the water would take the
shortest path and not go round the furthest radiators (or very little
So these valves need to be adjusted when the system is new, after that
that don't need to be touched.
(Called balancing the system)
If someone has messed about with even one of them, it could upset the
Eg if they opened one up fully that was close to the boiler, all the
heating water could go through that radiator and none through the
If you know someone has done this to a particular radiator, it needs
to be progressively closed until the whole system is warming.
But the whole system may need to be rebalanced if someone has been
messing about with several valves.
I can explain how you do this but you will need a tool to adjust these
valves. On some it's just a spanner.
Hot water systems I have had work like this. There are two main
controls (plus some safeties). the wall thermostat and the boiler
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
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.
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