Vaillant ecotec plus 428 fault code F72

[need2 knowmore]

I have had a Vaillant boiler installed for over 12months, it is open vented and heats both the radiators and the hot water cylinder. It was installed by a recommended competent heating engineer who has unfortunately recently left the area. The boiler worked fine thro' last winter. I did not use the heating thro' the summer and switched the heating back on 2/3 weeks ago and it was OK. However last week it was occasionally not coming on in the morning and was displaying Fault Code F72. I contacted a plumber and arrange for it's first service and mentioned the fault code, he told me to press the Reset which got the boiler working.
The plumber serviced the boiler and said he could find no fault with it, but said that he thought the fault was caused by the pipe work up to the Tees on the flow and return being only 22mm. He said it should be replaced with 28mm. but could not explain why the fault only happened occasionally and that the boiler worked OK up to a week ago.
I loked in the Vaillant manuals that had been left with me and the recommended pipe connections to the boiler are 22mm.
I don't think it is sludge restricting the pipes since most of the system was repiped when the new boiler was fitted and they were flushed out and inhibitor added.
I would like to get some independent advice on this problem before I go go to the expense of changing the pipework size because I believe that the boiler was installed and piped correctly to vaillant recommended instructions by a competent engineer.

 

[jtsplumbing]

Best to call Vaillant if you have any problems its still under warranty,

 

[happyflyer]

Like Jts say if its still under warranty get the manufactures back in, the only problem is they may well charge you if its not their fault.

F72 code is raised when the two thermistor one flow and on return have too great a difference between them, they are there to protect the heat exchanger from a low water flow there is no other way to test the water flow rate this is the cheapest known and well used method. If it is not faulty thermistors and you have no way of testing these AT ALL, what's happening is the water is getting to hot too fast and is not being removed from the boiler fast enough.

There are a few things you can check yourself, photos of the pipe around the boiler is always handy, what speed is the pump set at, do you have an intelligent pump with an inverter inside it, are all the zone valves fully open, try these first, what controls are there on the system.

Boiler with internal pump ???? check with manual about pump speed setting you cannot and must not open the boiler case up, I think it can be done through the keypad. Sure someone knows how to do if its not in the manual, this is a big problem with pumps inside cases
you can't adjust them and if it goes wrong you can't get one from Screwfix either.

Might be better to do what JTS said

 

[phil the bucket]

It's a wireing fault It has happened to me before boiler is constantly on running when hw and ch are satisfied it will carry on running through the bye pass then eventually overheat
then u will have to press the reset button
There is a link in the boiler that needs to be taken out

 

[jtsplumbing]

So Phil, are you saying that when in pump over run the burner stays on ?

 

[Nostrum]

428 doesn't have an integral pump as its open vent. I take it this boiler is fitted into a large house?

 

[Ermintrude]

Valve sticking and or bypass closed. Pump may be air locked or on its way. It's not a grundfos alpha pump is it....

 

[lame plumber]

pumps on its way out, had the same with a remeha ov boiler few years back and tried everything except the pump as owner insisted it was new, turned out he had a poor memory and a new pump pushed the water around quicker preventing the stats locking out.

 

[phil the bucket]

So Phil, are you saying that when in pump over run the burner stays on ?

Yeah it just passes through the bye pass then it will eventually overheat it happenes every morning because the boilers been on all night then u have to reset

I've made that mistake my self took me a few visits to relise what I did but u live an learn

 

[Ermintrude]

So is it wired correctly?

 

[happyflyer]

Ermi,

I ain't got a clue anymore I thought the pump was internal on that model but not so.

The OP man never came back to answer any questions, what do you make of that.

Those pumps with VSD built in need to be banned, they will come back to haunt you if you fit them and don't says it's in some obscure regulation
somewhere that you should it's your choice..????

 

[phil the bucket]

Get your gsr guy back to have a look

 

[happyflyer]

It's a wireing fault It has happened to me before boiler is constantly on running when hw and ch are satisfied it will carry on running through the bye pass then eventually overheat
then u will have to press the reset button
There is a link in the boiler that needs to be taken out

This is what the cus chap says The boiler worked fine thro' last winter. ????

 

[bert large]

If the boiler has not been electronically de-rated to suit the property size this can happen.
The boiler pumped out 28kw when the property only requires 15 or 18kw of output can leave too big a differential between flow & return on start up.
I know this sounds a bit odd but I have had it myself on exactly this boiler, after it had been installed for a year too.
These boilers are too clever for their own good if you ask me :/

 

[happyflyer]

Interesting that???

Can't agree more about clever boilers, one's from oversee in particular, I won't even buy French wine, I have a Worcester BOSCH, oh no !!

 

[Ermintrude]

Put it in auto!

 

[need2 knowmore]

Thanks to all you guys for your comments.
The system has 14 Radiators over 4 floors. The calculated Heat load inc. an allowance for Hw is about 20kw and the boiler output was set at this.
A further bit of info that came to me this morning is that it only occurs oaccasionally and always at the 1st switch on and the HW comes on 1st it has never happened once the boiler has run for a while.
What I don't understand, is that F72 is saying that the temp. difference between Flow and Return is not right, why then does it seem to happen at 1st switch on when when both pipes are cold and at the same temperature ?
Do the boiler electronics delay looking at the temperature difference until the Flow temp. has reach its set value ? If that is so then to me it looks like a boiler problem.
I am only trying to get to the bottom of this problem to save having to pay for possible uneccesary work on the system external to the boiler if the fault is in the boiler

 

[happyflyer]

"Do the boiler electronics delay looking at the temperature difference until the Flow temp. has reach its set value ? If that is so then to me it looks like a boiler problem."

I think not that would defeat to object of having the sensors looking at the temps, I asked you what the pumps was, I thought it was inside the boiler case, but someone thinks differently
they say that model the pump is outside the case if this is so can you look at it and tell us what it is.

We need to know more to help you, we are scratching the suface

 

[happyflyer]

The two sensors are there to protect the boiler from a low flow rate, if the flow rate is too low then the water temperature will rise too fast on the flow out to the system, this triggers the software to flag up an alarm
in this case F72, if you pump is taking to long to get up to speed the very first thing on start up, Bam!!!


This is getting to look like you are going to need to get the manufactures in and as I said if it's an external problem, £££££

 

[Leo21]

Put it in auto!

They don't like auto, they end up being under rated.

 

[need2 knowmore]

The pump is external, it is a Grundfos Selectric 15-60 and is set at 2. It is only about 12mnths old and when it runs it seems to circulate ok. As I said before it did not happen before, it only seems to happen at the 1st boiler switch on in the morning when the HW timer clicks on before the CH programmer clicks on, so the pump is only circulating thro the Cylinder. Could it be a problem with the Bypass valve?
Hope this helps. Thanks for your input.

 

[happyflyer]

Try and run the pump on 3

 

[Leo21]

Open/ check bypass.

 

[happyflyer]

Open/ check bypass.

Leo,

Come on its inside the boiler case, GSR

 

[lame plumber]

Leo,

Come on its inside the boiler case, GSR

should have an auto bypass on the system if its installed iaw building regs, another thought is whether the system was flushed through properly during the boiler swap, any crud in it and a new pump will stir it all up and ruin the pump in short shrift!