F72 error Vaillant Ecotec plus 418

[Mottie]

Our heating didn’t come on last night. I checked it this morning and the zone valve was 'clicking' when I turned the room stat up (as it usually does) but the pump wasn’t starting. I checked to see whether it was getting a feed when it should have and it had no feed. I then looked a the boiler (in the loft) and it showed a F72 flow/return temperature sensor fault. Searching on here led me to this post. I looked online and it showed how to clear faults by pressing a button on the front panel. I did this and it all fired up and is working fine now but what could have caused it in the first place? Could it be just a one-off or as the post I linked to, be a sign of the pump on the way out? There’s no undue noises coming from the pump but it must be getting on for ten years old now (Grunfos UPS2 15-50/60). I’m fairly confident it not, as the linked post also refers to, a blockage in the system. The pipework and valves were replaced about 6 years ago along with a power flush when the system was converted to a sealed one and it was again chemically flushed 4 years or so ago when the boiler was replaced. It’s got a magnetic filter and has always had inhibitor in it. The system water is crystal clear. Any suggestions?

 

[RayCaister]

In my expierence with Eco Tec Pro fault I opted for the Vailant Fixed Price repair , they replaced a number of sensors (only one of which was related to the fault) and the PCB . No problems since .

 

[Mottie]

Currently it’s still under warranty so I don’t want them just coming out and pressing a reset button like they did in the link I quoted above. It¡s all okay now so I’ll have to see if it does it again.

 

[Mottie]

Any other suggestions as to why it did what it did from heating engineers or Vaillant experts on here?

 

[CBW]

Any other suggestions as to why it did what it did from heating engineers or Vaillant experts on here?

I’ve heard from more experienced Vaillant experts that the ntc sensors rarely fail, so could be a few things, weak pump being one of them. F72 is flow and return temperature too great.

 

[Mottie]

I’ve heard from more experienced Vaillant experts that the ntc sensors rarely fail, so could be a few things, weak pump being one of them. F72 is flow and return temperature too great.

Thanks. I only run it on speed 1. If it happens again, I’ll replace the pump before looking further. What would you suggest I change it for - the same UPS2 or a replacement UPS3?

 

[CBW]

Wouldn’t necessarily just replace the pump as a matter of cause. Either pump if you are to replace is fine.

 

[Mottie]

It’s been fine since my last post but it’s just happened again! F72 fault. This time though pressing the buttons on the boiler says the fault has cleared but when I try to run it, it still says F72 fault flow/return sensor. When I call for either heat or hot water, after a few seconds, I hear a tiny 'click' in the airing cupboard where the valves and controller are (which is normal) but unlike normally, the pump doesn’t start a few seconds after that. Could it be the pump - I’ve checked it and it’s not seized?

Bit late to be messing about with it this time of night but if I test for a feed to the pump after I hear the 'click' tomorrow and it shows a feed, is it likely to be the pump? Boiler still under guarantee but I don’t want to call Vaillant out if it’s not the boiler. I think from memory the pump starts first and runs for a while before the boiler fires so could it be that it’s not sensing the flow and throwing up the fault code?

 

[Mottie]

Edit: I was pressing the wrong reset button! Pressed the correct one and it went through a menu that I just kept pressing 'next' and it fired up. Any idea what could cause this? This is the second time it’s happened now. I don’t want it happening again in the middle of winter as I might not be so lucky the third time!

Only thing I’m thinking is that I have always run my pump on speed 1 of 3 and I’m just wondering if, as the pump is getting older, it’s not as powerful now as it used to be. I’ve now got it running on speed 2 but do you think it could need changing? It must be 10 years old now so would you say it’s getting to that age?

 

[DP]

This boiler heat exchanger has high internal resistance.
The function of the pump is to circulate water ( hence at times called circulator)
There is a sensor on flow as well as return pipes
If you could mark a drop of water that enter the heat exchanger, is blasted by the fire and emerges from the boiler on its way to the load on its way to the heat load, two sensors are checking the flow and return. If the water flow is too slow, F72. Same goes for sensor fault ( rare) but that can be checked with additional temperature probes: slow pump is another.
In the first instance I would be getting the pump speed up and check the heat load for 20 degree differential

I think F72 is caused by slow pump speed
It will most likely by triggered during heating unless cylinder is far away

 

[Johntheo5]

Edit: I was pressing the wrong reset button! Pressed the correct one and it went through a menu that I just kept pressing 'next' and it fired up. Any idea what could cause this? This is the second time it’s happened now. I don’t want it happening again in the middle of winter as I might not be so lucky the third time!

Only thing I’m thinking is that I have always run my pump on speed 1 of 3 and I’m just wondering if, as the pump is getting older, it’s not as powerful now as it used to be. I’ve now got it running on speed 2 but do you think it could need changing? It must be 10 years old now so would you say it’s getting to that age?

If its not a faulty probe then F72 indicates that the flow/return dT is too great, it flags at arounnd a dT of 30C.
Could be any of the items above, also if you have a automatic bypass valve, ABV, installed, check its its index setting, should be ~ 0.48 at that UPS2 pump speed2, 5.0M.
Also check parameters d.40 & d.41, flow/return temps, especially for a minute or two immediately on fire up as these boilers fire up at ~ 65% of max output, if the dT is reaching 30C during this period then the flowrate would have to be as low as 5.59LPM, 335LPH, also check d.40/d.41 during normal running, these checks will give a very good indication of whats happening.

 

[Mottie]

If its not a faulty probe then F72 indicates that the flow/return dT is too great, it flags at arounnd a dT of 30C.
Could be any of the items above, also if you have a automatic bypass valve, ABV, installed, check its its index setting, should be ~ 0.48 at that UPS2 pump speed2, 5.0M.
Also check parameters d.40 & d.41, flow/return temps, especially for a minute or two immediately on fire up as these boilers fire up at ~ 65% of max output, if the dT is reaching 30C during this period then the flowrate would have to be as low as 5.59LPM, 335LPH, also check d.40/d.41 during normal running, these checks will give a very good indication of whats happening.

Thanks but that all seems like something I should leave for a heating engineer to check as I don’t really understand it! Currently it's running fine with the pump set at speed two. If it happens again, I may just change the pump first before getting Vaillant in to look at the boiler as it’s still got a couple of years left on the guarantee. If I did change the pump, would it be better to change it for a UPS 3?

 

[Johntheo5]

Its quite easy to check the d parameters, you just read them off, if the dT, the difference between d.40&d.41 is anything below 20C then you don't have a pump problem and might save you replacing it needlessly.

The UPS2 is more than adequate for a 18kw boiler, the UPS3 is a giant of a pump but can be run at the same pump heads as the UPS2. Personally, I would not install any pump in this day and age that does not at least display the power in watts, some now give the flowrate as well, very handy for trouble shooting.

 

[Mottie]

Personally, I would not install any pump in this day and age that does not at least display the power in watts, some now give the flowrate as well, very handy for trouble shooting.

If I were to replace it with such a pump, what would you suggest from the Grundfos range - an Alpha 1?

 

[Johntheo5]

I am not familiar with the Alpha range, I think the Alpha3L does display the power but not 100% sure, if not bothered with the power display etc I would be happier with the UPS2 (or UPS3).
I have a 4 year old Wilo Yonos Pico 6M (~ £125/135) which is a excellent pump IMO, it displays the power, the newer models also display the flowrate.