How does pump overrun work

Even though they're heavy duty devices, central heating circulating pumps do break down , and eventually they wear out. This usually takes fifteen years to happen, but it could happen sooner. Remove the lockshield 2. Open up the valves on all the radiators in the house by turning them anti-clockwise 5. Turn the central heating back on and note down the order the radiators heat up 6. Disconnect Electrical Wires. Turn off Inlet and Outlet Valves.

Disconnect the Old Pump and Remove. Insert new Pump and Connect up. Re-Connect the Electrical Connections. Test the New Pump. Either the room thermostat or the water cylinder thermostat calls for heat when the boiler turns on.

The diverter valve then directs the hot water to the radiator or the water cylinder as needed. Then the radiators will be hot even though the heat is turned off.

You do not have to live with constantly hot radiators. Why does my boiler say pump overrun? Category: home and garden home appliances. Pump overrun is a normal function of a heating system. After the boiler has been switched off, the pump circulates the water to dissipate any residual heat. If your pump runs for hours after the boiler has been turned off, there may be an issue in the system. Why is my boiler still running when thermostat is off?

Boiler still runs when thermostat is off. Should boiler pump run all the time? I think the "pump relay" you mention is actually the X I believe this now comes as standard with new Vaillant boilers, but didn't with mine, which is now 10 years old. The second pump after the llh should run with any demand eg hot water, heating or ufh.

SJB Plumber. Messages 2, Are you sure the second pump is actually running when theres a demand? Did you previously have HW priority before? The settings for this are I think D. Regarding the X40, yes you are probably correct. The newer Vaillants over a certain Kw have the relay built in now. Has the probe been for the cylinder been properly wired in?

SJB said:. To be clear about pump overrun, from memory, the boiler display shows a circle with a black triangle indicating the internal pump is running. To the left of this is a tap hot water supply active and the i button shows S. I also see this from time to time during the day, but instead of the tap, it is showing the radiator symbol in the display.

Again, the Grundfos pump is not on, so while in this mode, no hot water is being pumped around this system, even when the thermostats are calling for heat! Last edited: Jan 3, Is the pump on full speed? Could this not be a control fault ie PCB. The function of pump overrun is to dissipate the residual heat after a demand is satisfied to protect the boiler. It shouldn't be active at the same time as a demand, although obviously the internal pump will be.

I've just noticed the boiler is currently showing the radiator and pump symbol, but the new Grundfoss pump is not on. The system status is showing "heat. So, right now, there is demand by one of the zones, but the external pump is switched off and the internal boiler pump is running.

It's made a lot more noise than it should have done. One of the problems I've had is detailed on this page, so you can find out if this is happening to you. It isn't intended as a guide to fixing it, but rather to give you enough info so you can get the job fixed professionally.

Just keep bleeding the radiators as often as the noise appears. Apparently it's best to do this when the system is cold, or more air can be sucked in. There must be a better solution, but I don't know it yet. One interesting 'feature' of the system has been annoying me for a year. When the timer switches the heating off, the noise doesn't stop. On the contrary, the pump in the airing cupboard runs on My system switches off automatically at 9pm.

But I have heard the pump continue until midnight! After a tiring stressful day, being unable to shut the wretched thing off, when you desperately need peace and quiet, can be the last thing you need. The industry 'professionals' I brought in indulged as usual in a great deal of head-scratching and difficulty-making.

What is happening, is that when the heating switches off, the water is being pumped around the cooling radiators, without being heated. You'll see that the flame on the boiler has reduced to a pilot light, so no heating is going on. The water is being cooled by this process, which is perfectly normal - it is supposed to happen, for a short while, to allow the system to cool down.

Note that there is a knob on the boiler - mine is labelled with numbers - which determines how strong the heating is, and so how much gas is used. Higher values make for hotter water, which means warmer radiators, but also higher gas bills. Of course if you have the boiler knob turned up full, the water gets hotter, so it takes longer to cool - so always try turning that down first, if you want it to cool quicker. The process is controlled by a thermostat in the boiler - known as the pump overrun boiler thermostat.

Physically this consists of a control unit, about the size of a matchbox, with a long copper wire leading to a metal cigarette-sized object - the actual thermostat, which is plugged into a hole in the case. These things go wrong. Basically they lose their calibration, being heated and cooled, heated and cooled, every day for years. My previous house had exactly the same problem, which I was never able to resolve. In fact this problem probably affects all systems after a time.

These pump overrun boiler thermostats cannot be repaired - you have to buy a new one. I found that the part was listed in the manual that came with the boiler, but that it was best to get the gas-chappie to read it himself, otherwise he got confused, and hesitant, etc etc. They can get the part on next day delivery, so there really is no reason not to get it done. Just tell the guy that this is what you want, to deal with the pump overruns.

That's it. Simple, really. Which makes one wonder why the tradesmen make such a mountain out of a simple, easily diagnosable problem. Perhaps the best thing is to get them automatically replaced after 10 years the thermostats, not the tradesmen.

Now it may be that you want some quiet, but can't get around to fixing this just now. What can you do in the mean time? Firstly, I have an electric switch, in the kitchen next to the boiler, which controls all power to the central heating system, both boiler and pump.

In that case, the cause could be a wiring issue. The low-temperature switch could also be the reason for this issue. Tampering with wires can cause electrical hazards with most appliances. We always suggest you contact a gas-safe engineer to solve the problem. They may even examine the shut-off temperature controls. They would pay special attention to the low-temperature switch.

These are some reasons that can be responsible for the overrun issue of your central heating pump. We hope you get your Gas Safe engineer as quickly as there is an issue! Question: Is it good having a pump overrun? Answer : Pump overrun is required in most modern heat-only boilers to remove leftover heat. It also prevents the possibility of water boiling in the heat exchanger when turned off. The majority of manufacturers mitigate this danger by utilizing a pump overrun. Question: How do I amend the ignition lockout on a boiler?

Answer : When you observe a red light flashing or consistently glowing, you know your boiler is locked out. Turn the temperature control knob entirely counter-clockwise to reset. Hold your breath until the red light turns off. Return to your previous setting. Question: Is the central heating pump overrunning for a while okay?