Target Flow Temp Exceeded

[Dunbar]

My boiler (Vaillant eco-Tec +418) was installed around 18 months ago and has been working fine.

However, I recently noticed that the target flow temp is being exceeded.

We control room temp via the room stat, so whilst it is on at the programmer, the CH obviously doesn't come on this time of the year.

The flow temp is set to 60, but when it comes on to heat water, it keeps going until the reading is 65. The tank stat is set at 55. The boiler was not set for cylinder charging.

Would be grateful for comments and advice. Should I be concerned.

Many thanks.

 

[ShaunCorbs]

The boiler was not set for cylinder charging ???

 

[Dunbar]

Yeah, that is correct. When I press the button underneath the tap icon I get a flashing message 'cylinder charging off'. The fitter said we didn't need it on, so assumed that the diverter valve would operate to ensure cylinder was full of hot water, and cylinder stat would keep the hot water to required temp. Didn't have enough knowledge to argue with him, but expected the boiler to heat water on flow to what I have set. i.e 60 and not 65.

 

[doitmyself]

Which cylinder thermostat do you have?

 

[Dunbar]

It's one of those basic Drayton jobs that wraps around the tank. I've set it at 55.

 

[doitmyself]

So the cylinder stat has no way of telling the boiler what temperature it should run at. Which makes me think that there is a 5C tolerance built into the boiler - mine (not Vaillant) has the same.

At the moment you have the boiler set to 60C and want the HW cylinder heated to 55C. Normally there should be a 10-15C difference, so the cylinder heats up faster. Also the recommended cylinder temperature is 60C - it kills off any legionella present.

 

[Dunbar]

Thanks for the info. I managed to get hold of the fitter on the phone this afternoon and he said, 'No that is fine, it’s just the boiler modulating the burn as it should do'.

Re the cylinder stat, I note that it's wired into a junction box, as is the programmer, diverter valve and pump.

 

[doitmyself]

I would expect the cylinder stat, programmer etc to be connected to a junction box; the boiler will also be connected to the box. The cylinder stat is just a temperature controlled on/off switch. All it can do is tell the boiler to turn on or off; it can't tell it what temperature to run at. For that you would need more sophisticated controls.

 

[Dunbar]

Thanks for the info and advice.