Boiler with no pump overrun

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 .
--
Gypsygirl


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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.
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Gypsy Girl:
Read my post in the thread entitled "Bleeding Hot Water Radiators - Conflicting Instructions".
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.
--
nestork


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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 warm .
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 .
--
Gypsygirl


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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 anyway).
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 whole system. 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 others. 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.
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On Mon, 21 Jan 2013 13:56:19 +0000, Gypsygirl

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.
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On Tue, 22 Jan 2013 17:16:22 -0500, Paul Franklin

That was my guess too. Either wired wrong or a failed control.
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Okay , by the sounds of it its not going to be an easy fix. Will take your advice and get a proffesional to look at it . Thanks for all your suggestions .
--
Gypsygirl


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