Vaillant boiler always exceeds set temperature

[kilodelta]

Hello. I have a Vaillant EcoFit boiler that is a few years old. We had our annual service last month and ever since then I’ve noticed something unusual.

The radiator mode temperature is set to 65C but it always exceeds that, hits 70C, and then stops and the the egg timer comes on. If I check the boiler status, I see either S.07 (pump overrun) or S.08 (anti cycling mode).

Is this normal? I called the engineer and he said it was. I’ve noticed the egg timer would sometimes come on if the Nest turned the heating on and off in quick succession, but not every time it fires up.

Thanks.

 

[kilodelta]

@John.g This is still happening Is the boiler supposed to regulate its temperature so that it maintains flow temperature? If so, why isn't this happening?

If I only have 6 radiators on, can I reduce the the KW from 16 to something even lower?

 

[John.g]

There can be two reasons for this, one is that the boilers minimum output is greater than the heat demand from the rads, in which case the burner will cut out when the flow temperature exceeds the boiler setpoint temp by 5C. The other reason is if the burnercuts out within a minute or two of firing up if the boiler hasn't modulated down fast enough. You can try I creasing the boilerflow temperature to 75C or more and yes you can kw from 16kw to say 8kw, might help

 

[kilodelta]

Thanks! I’ve noticed something different. The issue only seems to happen when the Nest has the hot water on. The hot water goes to an unvented cylinder.

When the radiators are on, the 64C is maintained. When they are off but the unvented cylinder is heating, the boiler turns on, goes straight to 70C, cuts off, then repeats over and over again. is the unvented Cylinder broken? I thought if the water was on but it was at temperature, it would trigger the boiler to go on.

 

[John.g]

The HW (unvented cylinder ) temperature setpoint temperature should always be set lower than the boiler water temperature, ideally by 10C lower but certainly at least 5C lower.

 

[ShaunCorbs]

Reduce the boiler output to 6 or the lowest you can do

 

[kilodelta]

The HW (unvented cylinder ) temperature setpoint temperature should always be set lower than the boiler water temperature, ideally by 10C lower but certainly at least 5C lower.

The attacher is on the cylinder… it’s set to 65C (I think it always has) and this is higher than the boiler flow temperature. This should be dialed down 5-10C?

 

[ShaunCorbs]

The attacher is on the cylinder… it’s set to 65C (I think it always has) and this is higher than the boiler flow temperature. This should be dialed down 5-10C?

Boiler should be 65 cylinder stat wants reducing to 60

 

[kilodelta]

Still happening with the boiler set to 64 and the cylinder to 50.

What is the expected behaviour? Is the boiler supposed to turn off when the cylinder signals it’s at temperature (but the Nest indicates it’s still on, waiting to signal
To the boiler that it needs to heat its water?)

Should I call an unvented cylinder engineer or should I try reducing the boiler to 8KW?

 

[ShaunCorbs]

Nest will still signal it needs heat as they don’t talk to each other the stat controls the temp

 

[kilodelta]

So as long as the Nest has the hot water on, the boiler be on to heat the water in the cylinder? What happens when the cylinder’s water reaches the cylinder’s set temperature?

 

[ShaunCorbs]

Once the nest is set for water on eg calling the cylinder stat takes over and controls the temp

 

[John.g]

Suggest running off say 10 to 15 litres of HW with tap opened for 5 minutes or so, then programme the CH + the HW to come on together then switch off the CH only after 3 or 4 minutes and see if the boiler continues to fire until the cylinder is fully heated.

 

[kilodelta]

Thanks for all your help everyone. The house is thankfully warm and we still have hot water so I can’t complain at the moment, even if it doesn’t seem to be operating as it should.

I dropped the power to 8kW to see how things runs.

I assume it’s safe to play with the power output?

 

[ShaunCorbs]

Yes as it’s just settings will soon tell you no if it doesn’t like one

 

[V1ks44]

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

Attaching photo of the UFH located under my stairs, i cant rem for 100% the loop lengths of the pipe run. Kitchen is split in into 2 circuits i know one was about 70m and the other was about 30-40m. Same with the living room they were about 75m each.

I have been playing around with the Flow rates recently but at present they are set to around 3l and pump speed to 3. I have recently tried to have the rates at around 2l with the pump speed on 2 but the kitchen seem to take a very long time to warm up due to higher heat loss because i have very large 3 panel bifold doors.

Let me know if u need any other info...ill try my best to get this..