Advice really appreciated on hot water temperature

[JanetD123]

Hello people in the know! I have just moved into a new house. It is a system I am not used to as my previous home had a combi boiler. So, there is a large blue hot water cylinder in the airing cupboard and the dial on the front is set to 65. There is a Valiant Ecotec 418 Boiler in the kitchen and the water dial is set to 65 (it doesn't go higher than this).
I have the water set on a timer to come on at 5pm for one hour.
It just doesn't seem hot enough. So . . . can I turn up the temperature on the front of the blue hot water cylinder or is it governed by the 65 setting on the boiler. Also, how long should the water stay hot for? The system was installed by the previous owner in 2014.
Many thanks for any advice you can give. All the best Jan

 

[fezster]

I was talking about the settings on the dial itself. I had taken it that you meant the dial will not turn up past 65 degrees. On the Vaillant boiler you can alter the maximum setting the dial will go to. Meaning that if you turn the dial fully clockwise until it stops, the max temp you can set it too was 75 from the factory but that setting can be altered from 40-80 degrees.
Can you turn the CH dial to 75?

I believe OP has said it's the HW dial they are trying to adjust.

As you say, the CH dial can be adjusted to 75 from the factory and also modified through the installer menu to allow higher.

The HW dial will be restricted to 65 as it is used to control the cylinder temperature (if used with Vaillant controls). I can't remember just now (and I'm not in front of my boiler) but I think the HW dial is only restricted to 65 if and when a VR10 is attached.

OP - can you please confirm (or take pictures) of the various controls you have, as this will determine whether it's the HW dial or the Radiator dial you need to be adjusting on your boiler.

 

[JanetD123]

OK - pic attached - the HOT WATER DIAL ON THE BOILER only goes up to 65 and that is what is it set to. The CH DIAL ON THE BOILER is set to 57. Shall I increase the CH DIAL ON THE BOILER AS THIS DOES GO UP TO 75 - thank you. Jan 🙂

I believe OP has said it's the HW dial they are trying to adjust.

As you say, the CH dial can be adjusted to 75 from the factory and also modified through the installer menu to allow higher.

The HW dial will be restricted to 65 as it is used to control the cylinder temperature (if used with Vaillant controls). I can't remember just now (and I'm not in front of my boiler) but I think the HW dial is only restricted to 65 if and when a VR10 is attached.

OP - can you please confirm (or take pictures) of the various controls you have, as this will determine whether it's the HW dial or the Radiator dial you need to be adjusting on your boiler.

 

[fezster]

OK - pic attached - the HOT WATER DIAL ON THE BOILER only goes up to 65 and that is what is it set to. The CH DIAL ON THE BOILER is set to 57. Shall I increase the CH DIAL ON THE BOILER AS THIS DOES GO UP TO 75 - thank you. Jan 🙂

Can you take a pic of your wiring centre (wall mounted box near boiler with wires going into it)? And your thermostat?

 

[JanetD123]

Will post pics as soon as I am home - thank you

 

[Ric2013]

Is it just me that thinks it utterly ridiculous to have a HW dial that might not be doing anything unless an extra control is fitted? Must be one of the least intuitive examples of product design ever.

 

[fezster]

EEEk where is the wiring centre?

Take a pic of the thermostat - that will tell us if it's a Vaillant ebus control or not

 

[JanetD123]

Hi guys. OK I've attached a pic of thermostat on HW cylinder, CH thermostat in hall and programmer in airing cupboard.
I have not touched the boiler temps eg: HW 65 and CH57.
Now you have seen the controls do you thinks I should up the CH temperature dial on the boiler Fezster?

Many thanks Jan

 

[fezster]

Standard controls, so increase the rad dial on the boiler to 75. The cylinder should heat up within an hour or so and the hw too hot to touch under the tap.

 

[JanetD123]

Standard controls, so increase the rad dial on the boiler to 75. The cylinder should heat up within an hour or so and the hw too hot to touch under the tap.

Thanks Fezster . . . so if I have the HWCylinder thermos at 60 and the HW dial on boiler at 70 would that be ok too?

 

[JanetD123]

Standard controls, so increase the rad dial on the boiler to 75. The cylinder should heat up within an hour or so and the hw too hot to touch under the tap.

Yayyy - I have roasting hot water. So I am guessing my boiler temps (CH &HW) need to be 10 degrees higher than my HWcylinder temp - thank you x

 

[Chuck]

Yayyy - I have roasting hot water. So I am guessing my boiler temps (CH &HW) need to be 10 degrees higher than my HWcylinder temp - thank you x

Based on several days of experiments on with a data-logger recording thermocouple readings of my unvented cylinder temperature and flow and return pipes for its cylinder coil I concluded that the minimum that one can get away with is to have the boiler (flow) temperature 5°C higher than the tank set point. So a 10°C difference is a good choice.

 

[fezster]

Good to hear its sorted. Roughly 10 degrees, I've found. Though you may get away with lower. The higher the differential, the faster the heat transfer, and the quicker your cylinder will heat up. This is why vaillant controls boost the flow temp to 80 degrees automatically when heating the cylinder, so that there is minimal disruption to heating.

 

[johnduffell]

You can get eco ones where it starts with a lower flow temperature to give good condensing and gradually ramps up as the return temperature increases. I think that is basically a more optimal balance between speed and efficiency, it does take a percentage longer but nothing excessive.

 

[fezster]

A condensing boiler will work to a 20 degree flow/return differential. So when heating the cylinder alone, the return temperature will increase as the water inside the cylinder heats up. Whilst the return temp is under 55 degrees, you will get the benefits of condensing. Only for the last part of the cycle (to get the cylinder to 60 or 65) will the boiler not be condensing.

I'm pretty sure every boiler works this way, so not sure what "eco" refers to in this context?

 

[johnduffell]

A condensing boiler will work to a 20 degree flow/return differential

It will, and that's the recommended design drop for new systems, but it will also work to other temperature differences depending on the conditions present in the system.

Whilst the return temp is under 55 degrees, you will get the benefits of condensing

condensing isn't a binary thing like that, there's a lot of energy returned in the condensation, over 10% more. It's the flue gas temperature the matters most.

so not sure what "eco" refers to in this context

IfI have to look it up as i don't know the details, but it just seems very implausible that controlling the flow temperature to a fixed value could be the most efficient way to heat a cylinder. But it certainly sounds like the quickest way.

 

[dan_the_plumber]

Get your Gas safe engineer to gas rate the boiler to check it’s burning enough gas. I can’t tell you exactly what that might mean, but could be a simple boiker component replacement

 

[johnduffell]

not sure what "eco" refers to in this context?

I did try to look it up but can't find it any more, sorry about that.

 

[SJB060685]

Yayyy - I have roasting hot water. So I am guessing my boiler temps (CH &HW) need to be 10 degrees higher than my HWcylinder temp - thank you x

If the boiler temperature is lower than HW stat you will never desired hot water temperature, that’s how these things work. It’s thermal equilibrium