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

 

[Aire]

The cylinder thermostat should be set at 65° so no need to change that. Your likely not timing your hot water for long enough. How big is the cylinder?

 

[JanetD123]

Hi Chris - thank you for your reply. Its a big one! (see pic) My neighbour has had a look and says the pipe to the tank from the 3 port valve(?) is hot so thinks my boiler is faulty - but he's not a gas engineer so I wanted to get some advice before calling out an engineer

 

[snowhead]

Ah, another Brexit stockpile...

How hot does the water get, hand hot or colder?
What time are you trying the water?

As per Craig, it's not on for long enough if it's only on for an hour a day.

If you need it for 5pm, try setting the timer for 3.30pm and see when it gets hot enough.
Adjust the time if you think it's too early.

 

[JanetD123]

LOL @ Brexit stockpile! Hand hot but not hot enough that I need to pull my hand away.
My sister has a similar system but only has her water on for half an hour and its roasting! Ho hum.
Thanks snowhead . . . will try to put it on for longer

 

[SimonG]

Run it longer, once up to temp it will shut off.

 

[Aire]

Hi Chris - thank you for your reply. Its a big one! (see pic) My neighbour has had a look and says the pipe to the tank from the 3 port valve(?) is hot so thinks my boiler is faulty - but he's not a gas engineer so I wanted to get some advice before calling out an engineer

Hi Jean you don't have a 3 port valve, you have zone valves. When the timer is calling for hot water then the pipe should be hot to the cylinder, if your hot water isn't on but your heating is then it could also be convection heating the pipe up. If your unsure or concerned then best to call an engineer in to check the system over.

 

[JanetD123]

Thanks Simon G - will try the 1.5 hours as Simon suggested . . . Craig . . . I just let him come in for a look in case it was an easy fix, but tbh I probably wrote it down wrong! Thanks guys, really appreciate your help

 

[johnduffell]

if the boiler only supplies water at 65c the cylinder would take a while longer to get up to temperature, traditional boilers would go up to 80+. If that's as high as it goes you'll have to give it plenty of time.
However having said that all the pipes around the valve should be red hot when it's running so it could be either a circulation or a valve issue.

 

[rpm]

Not trying to get you to spend money however when was it last serviced? Maybe a service and a full explanation of what`s what would help you.

 

[fezster]

The water being 'hot enough' is subjective. You could measure the temperature at the hot tap - it will probably be roughly 10 degrees lower than the cylinder is set to, because of heat loss before it gets there.

If your boiler is only set to 65 degrees, though, it'll short cycle before the cylinder has fully heated up. The boiler flow temperature should be roughly 10 degrees higher than the cylinder stat temperature to allow adequate heat transfer.

 

[Welder]

if the boiler only supplies water at 65c the cylinder would take a while longer to get up to temperature, traditional boilers would go up to 80+. If that's as high as it goes you'll have to give it plenty of time.
However having said that all the pipes around the valve should be red hot when it's running so it could be either a circulation or a valve issue.

It's the cylinder stat that's set to 65 not the boiler

 

[chris watkins]

Janet has your Vaillant got the two temperature dials on the front (one Rads & one Tap) if so what temperature do you have set for the rads ??

 

[chris watkins]

The hot water (tap) dial on your boiler has no effect, it is not used in this country on the regular or system boilers only the comb's.
You will need to have the heating (rad) one turned up to at least 70 so it can heat the domestic hot water up to the required 60 -65 deg C.

 

[johnduffell]

It's the cylinder stat that's set to 65 not the boiler

A can't disagree, I was just taking the op on face value that there were two and both set to 65c!

or is it governed by the 65 setting on the boiler

there is a large blue hot water cylinder in the airing cupboard and the dial on the front is set to 65.

 

[fezster]

The hot water (tap) dial on your boiler has no effect, it is not used in this country on the regular or system boilers only the comb's.

Unless paired with a VR65/VR66 and VR10 sensor, in which case the HW dial directly controls the set temperature of the cylinder. And the flow rate is automatically boosted to 80 degrees when heating the cylinder.

I agree, though, that unless the Vaillant controls and sensor have been adapted to work with a non-Vaillant Unistor cylinder, the radiator dial on the front of the boiler will control flow temp to the cylinder and must be set approx 10 degrees higher than the cylinder stat.

 

[Last Plumber]

Going back to what @johnduffell mentioned.
The target temperature of the cylinder is the same as the max temp of the boiler. Therefore the cylinder will struggle to get there due to the fact that there are heat losses. The coil / heat exchanger in the cylinder needs to be hotter than the water temperature you're aiming at otherwise it will never reach it, or it may do over time.

The Vaillant boiler maximum temperature on the stat can be altered. They come factory set to 75 but will go up to 80 or down to 40.
You may want to get a Gas Safe Engineer to service it and check it over and then raise it back to 75. You could raise it yourself I have no doubt but there may be a reason the previous owner set it so low?

Hope this helps.

 

[JanetD123]

Hello - thank you for all your replies. The boiler was last serviced in October 2018. The water temp on BOILER is set to 65 and the rads temp on BOILER is set to 57. The thermostat on the front of the HWcylinder is set to 65. I've upped the timer to 1.5 hours.

 

[fezster]

and the rads temp on BOILER is set to 57. The thermostat on the front of the HWcylinder is set to 65. I've upped the timer to 1.5 hours.

With the boiler set to 57, the Cylinder stat will *never* be satisfied. You need to set the boiler to 75.

This is one of the compromises of having a cylinder which requires a high flow temp and a CH system which can run on much lower flow temps. The only way around this is to use the Vaillant controls or OpenTherm controls (though your boiler would require a separate OpenTherm module for this).

 

[Last Plumber]

Hello - thank you for all your replies. The boiler was last serviced in October 2018. The water temp on BOILER is set to 65 and the rads temp on BOILER is set to 57. The thermostat on the front of the HWcylinder is set to 65. I've upped the timer to 1.5 hours.

The Water temp dial on the Vaillant will not work unless you are using the correct Vaillant controls. I must have skim read the post as I did not see 57 deg mentioned earlier. As @fezster says, if boiler flow temp is below the target cylinder temp, it cannot get the cylinder up to the required temp.
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?
If so try setting it on that for a day or so to see if it does the job. If it does, ask an Engineer to look at the set up of the system. You don't really want higher temperatures with a condensing boiler if you can help it. They will be less efficient on the Heating side.

 

[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