Vaillant boiler always exceeds set temperature.

[V1ks44]

Hi sorry to hijack the thread, but im new to these forums and upon searching for some answers to my below question i come across this thread.

I have a vaillant 637 system boiler which is located in my loft eaves and has a hot water tank (180L) connected to it which is next to the boiler. The boiler is has 3 zone valves >>1. Heating radiators located in the first floor 4 rads + 2 towel rads. 2. UFH which heats the entire ground floor via 4 port manifold (set to 50c at the thermostatic valve). 3. valve for the Hot water tank (this comes on twice a day for 1 hour).

The boiler flow temp is set to 60c.

Because of my UFH i have kept the flow temp to 60c and i find heating the rads at this temp is good enough because only 2 rooms are heated most times.

I have had this setup for 2 years however recently i had issues with air in the system and went online for answers and whilst reading i read alot about the flow and return temps on some other forums.

Q1 when the UFH or Rads are calling for heat the boiler will fire normally, get the water to the required flow temp to the manifold/rads. However when i check the boiler screen, for good 4 min (timed) the ignition screen will come and then after the boiler goes into the egg timer (Anti cycling time) until the temp drops to around 40c and then it will fire up again back to 60c+. I do find the Flow temp overshoots above 60C by 5c then will come back down.

Doe the photos below indicate that the boiler is working as expected and this is normal behaviour, is the boiler condensing? If not is it possible to change the kw of the boiler to a lower value?

The other thing i noticed in the Diagnostic menu >> D.41 >> Return temp is only 5C difference to the flow. So when the flow is set to 60C the return is 55C >> is this normal because i have read on many forums that boilers dont condense unless the return temp is below 54C and therefore its not running efficiently and energy is wasted?

I am just trying to get my head around all this and if this setup will cause me issues with the boiler in the long run if its not condensing as it should.

happy to provide more info if required...

 

[ShaunCorbs]

Can you do a test just run the heating No ufh as normally it’s the ufh that causes problems with vaillants

 

[V1ks44]

Can you do a test just run the heating No ufh as normally it’s the ufh that causes problems with vaillants

Thanks for the reply, let me test that now and will report back, i assume you want me to let you know im getting the same thing on the boiler screen i.e firing and the anti cycle timer?

i forgot to add the Central heating + Hot water is controlled via Hive and the UFH is via Solfex Neo app, where the hub is paired with the heatmiser wiring cent.

 

[V1ks44]

So after running the heating for 30min the boiler on the screen was showing the attached screen and then once it hit 60c, I heard the zone valve for Heating made a noise and the hive receivers central heating light flashed for about 10 seconds and then went solid. And during this time the screen on the boiler then went into the Anti cycling mode where the temp kept going down from 60c until it reached 47c with the egg timer flashing and heating icon solid. The boiler was not running now while the timer icon still flashing away and then the boiler fired back with the temperature increasing from 47c with the heating icon flashing.

Just a note:

I do have hive TRV on each of the 4 rads which all were set to 19c for this test and the room temp at the time was 16c.

 

[ShaunCorbs]

So it ran 30 mins without a problem and then turned off and egg timer was present?

 

[John.g]

Or is it taking the boiler 30 minutes to reach 60C, it then goes to recycle?

 

[V1ks44]

Yes 30min and then it did start again after that brief moment where it stopped completely...with firing up again as it would when your turn it on for the first time from cold.

 

[V1ks44]

Or is it taking the boiler 30 minutes to reach 60C, it then goes to recycle?

So I turned off the UFH off after my post and then it took 30min to hit 60c and then did what I mentioned above...

I assume that it would do that again until the rooms reach the set temp which I had set to 18c.

Right now CH is off now as rooms have reached the temp and as my ground floor is getting cooler due to the cold outside l so I've turned on the UFH.

 

[John.g]

The only reason I can think of for taking so long to reach 60C is that the output is range rated to some low kw setting, even so, the boiler shouldn't go to recycle until 65C, (60+5)?
What we're the return temps during this 30 min heating period?

 

[V1ks44]

The only reason I can think of for taking so long to reach 60C is that the output is range rated to some low kw setting, even so, the boiler shouldn't go to recycle until 65C, (60+5)?

This is what I'm trying to understand, is that once it hits the target flow temp what should happen for a normal boiler if we assume mine is not set correctly.

I was looking at the manual was thinking if I change the d.0 setting from Auto to x kw would that make a difference if we are saying that it should not anti cycle after it hits 60c. Currently is auto but when I checked earlier i can go as low as 6kw but Im scared to change anything Incase I end up screwing up the boiler.


I see this was suggested to someone with the 630 boiler but I understand they had some error on their screen whereas I don't have anything.

Or consider getting a vaillant engineer to come and check my setup to make sure everything is ok.

 

[ShaunCorbs]

Do you have the spec for the ufh / what flow rates do the ufh flow meters show with everything on / calling ufh wise ?

 

[John.g]

This is what I'm trying to understand, is that once it hits the target flow temp what should happen for a normal boiler if we assume mine is not set correctly.

I was looking at the manual was thinking if I change the d.0 setting from Auto to x kw would that make a difference if we are saying that it should not anti cycle after it hits 60c. Currently is auto but when I checked earlier i can go as low as 6kw but Im scared to change anything Incase I end up screwing up the boiler.


I see this was suggested to someone with the 630 boiler but I understand they had some error on their screen whereas I don't have anything.

Or consider getting a vaillant engineer to come and check my setup to make sure everything is ok.

Suggest changing the Kw from Auto to 6kw, also the anticycle time d.002 might have to be increased from its present settiung of 20 mins, you should see a table somewhere that gives the actual anticycle time as it looks at the target flow temp and the set anticycle time to give the actual time.