PDHW dual temperature using EPH CP4

[Cleph]

I've recently had a new Ideal boiler installed (Ideal Logic Max Heat 2 H18) and plumbed for PDHW (priority hot water). I use it with EPH CP4 series: CP4i, additional Combipack 4, CP4-HW-OT, wired and configured as per EPH instructions, covering downstairs, upstairs and hot water tank, with the boiler controlled using OpenTherm.
The boiler target flow temperature is set on the master CP4 using HHbO (t-5) in the OpenTherm parameters and the boiler display shows that this is working.
However, for PDHW the aim is to use a lower boiler target flow temperature when running central heating (e.g 55°C) to keep the boiler in condensing mode and higher when heating the hot water tank (e.g. 69°C) to get the tank above the Legionnaires temperature. Unfortunately the EPH set does not support dual temperatures, so I set HHbO to 55°C and use a relay across the OpenTherm wires when HW is on, which causes the boiler to run at its set flow temperature (69°C).
This produces the desired result, but is a bit naff (and the boiler display is wrong when heating HW). Has anyone found a better way?

 

[MNW67]

Are you talking about the setup below?

Have you emailed EPH technical support to ask how it is supposed to work? This diagram doesn't seem to mention a relay. I have only ever read about this type of setup, but had assumed the hot water cylinder temperature and the hot water flow temperature were set on the programmer and were then somehow transmitted to the boiler on the OpenTherm connection.

Above my pay grade, but I have noticed P06 and P08 settings which talk about setting DHW temperature.

I think I've read elsewhere that the Ideal Logic has built in PDHW support and doesn't need to use the EPH controls.

@muggles and @vulcancontinental and @Sim777 may be able to advise.

 

[old duffer]

I've recently had a new Ideal boiler installed (Ideal Logic Max Heat 2 H18) and plumbed for PDHW (priority hot water). I use it with EPH CP4 series: CP4i, additional Combipack 4, CP4-HW-OT, wired and configured as per EPH instructions, covering downstairs, upstairs and hot water tank, with the boiler controlled using OpenTherm.
The boiler target flow temperature is set on the master CP4 using HHbO (t-5) in the OpenTherm parameters and the boiler display shows that this is working.
However, for PDHW the aim is to use a lower boiler target flow temperature when running central heating (e.g 55°C) to keep the boiler in condensing mode and higher when heating the hot water tank (e.g. 69°C) to get the tank above the Legionnaires temperature. Unfortunately the EPH set does not support dual temperatures, so I set HHbO to 55°C and use a relay across the OpenTherm wires when HW is on, which causes the boiler to run at its set flow temperature (69°C).
This produces the desired result, but is a bit naff (and the boiler display is wrong when heating HW). Has anyone found a better way?

for less money you could have had a state of the art Japanese system that would have provided just what you want....

 

[MNW67]

for less money you could have had a state of the art Japanese system that would have provided just what you want....

Sounds interesting. Do you have some details?

 

[Notch7]

I've recently had a new Ideal boiler installed (Ideal Logic Max Heat 2 H18) and plumbed for PDHW (priority hot water). I use it with EPH CP4 series: CP4i, additional Combipack 4, CP4-HW-OT, wired and configured as per EPH instructions, covering downstairs, upstairs and hot water tank, with the boiler controlled using OpenTherm.
The boiler target flow temperature is set on the master CP4 using HHbO (t-5) in the OpenTherm parameters and the boiler display shows that this is working.
However, for PDHW the aim is to use a lower boiler target flow temperature when running central heating (e.g 55°C) to keep the boiler in condensing mode and higher when heating the hot water tank (e.g. 69°C) to get the tank above the Legionnaires temperature. Unfortunately the EPH set does not support dual temperatures, so I set HHbO to 55°C and use a relay across the OpenTherm wires when HW is on, which causes the boiler to run at its set flow temperature (69°C).
This produces the desired result, but is a bit naff (and the boiler display is wrong when heating HW). Has anyone found a better way?

Could you not use weather compensation to set the boiler heating?

I’ve just had a PDHW setup installed with an Ideal Vogue max gen 2 with Ideal weather comp, it also has 2 switched lives one for hot water, one for heating.

Over the last few days the heating has been typically running at around 44 deg C flow and a return of around 38 deg.

Hot water flow runs at 80 deg and tank stat set at 55 ish (heats to about 60c)

 

[Cleph]

Are you talking about the setup below?

Have you emailed EPH technical support to ask how it is supposed to work? This diagram doesn't seem to mention a relay. I have only ever read about this type of setup, but had assumed the hot water cylinder temperature and the hot water flow temperature were set on the programmer and were then somehow transmitted to the boiler on the OpenTherm connection.

Above my pay grade, but I have noticed P06 and P08 settings which talk about setting DHW temperature.

I think I've read elsewhere that the Ideal Logic has built in PDHW support and doesn't need to use the EPH controls.

@muggles and @vulcancontinental and @Sim777 may be able to advise.

Thanks for your reply - yes, it's as the setup you showed, but with two CH zones (an additional CP4) and yes, I've been in contact with EPH tech support. You are correct that P06 seems to offer DHW temperature control, but this doesn't actually affect the temperature that the CP4 sends to the boiler over OpenTherm - the CP4 always requests what I've set in HHbO (55°C) and the boiler is quite good at keeping to that. But to get the hot tank water to 55-60°C you need 65-70°C flow temperature.

 

[Cleph]

Could you not use weather compensation to set the boiler heating?

I’ve just had a PDHW setup installed with an Ideal Vogue max gen 2 with Ideal weather comp, it also has 2 switched lives one for hot water, one for heating.

Over the last few days the heating has been typically running at around 44 deg C flow and a return of around 38 deg.

Hot water flow runs at 80 deg and tank stat set at 55 ish (heats to about 60c)

Thanks for your reply. Yes, there is an SL2 on the boiler, but no information is given about this in the installation manual and it is labelled as Frost Stat Optional. So on this model it doesn't appear to be a switched live for HW. I tried asking Ideal what it does, but they would not reply to me.

 

[MNW67]

Thanks for your reply. Yes, there is an SL2 on the boiler, but no information is given about this in the installation manual and it is labelled as Frost Stat Optional. So on this model it doesn't appear to be a switched live for HW. I tried asking Ideal what it does, but they would not reply to me.

Pages 4 and 5 appear to show the wiring for using SL2 on the Logic. The guide doesn't specifically say it covers Logic 2. But what is the point of having a weather compensation connector on Logic 2 if it can't do PDHW? The flyer for Logic Heat 2 definitely says that it does weather compensation. And anyway, why would a frostat need a separate switched live. It's all very strange but it could just be a mistake. I have found quite a lot of mistakes in various installation manuals. The wiring itself looks quite different to the Vogue wiring.

The best way to get the information from Ideal might be to ask them how to do weather compensation on your boiler.

https://idealheating.com/uploads/documents/Weather_Compensation_Kit_User_Guide.pdf

Thanks for your reply - yes, it's as the setup you showed, but with two CH zones (an additional CP4) and yes, I've been in contact with EPH tech support. You are correct that P06 seems to offer DHW temperature control, but this doesn't actually affect the temperature that the CP4 sends to the boiler over OpenTherm - the CP4 always requests what I've set in HHbO (55°C) and the boiler is quite good at keeping to that. But to get the hot tank water to 55-60°C you need 65-70°C flow temperature.

So, did EPH advise how best to make it work? Is the relay method you currently have the official way of doing this? I also thought it would be less clunky!

 

[old duffer]

Sounds interesting. Do you have some details?

Rinnai is the largest heater manufacturer in the world. https://www.rinnai.com/en They have an office in the north west but its cheaper to buy from one of the distributors.

 

[old duffer]

Sounds interesting. Do you have some details?

https://www.rinnai-uk.co.uk/product...ted-gas-fired-commercial-water-heater-w1600in is the commercial side. I use the domestic model as I also have a rinnai combi that provides for another shower

Hydrogen and BioLPG ready condensing water heaters

The condensing N Series 30% Hydrogen blend ready continuous flow water Heaters utilise market leading patented technology to deliver cutting edge efficiencies and performance. Stainless-Steel Primary

www.rinnai-uk.co.uk

Rinnai BioLPG and Hydrogen blend ready water heaters

Rinnai Gas Multi-Point 17i Low NOx Internal Water Heater Revolutionise and go continuous flow with Rinnai high efficiency Low NOx multipoint water heaters. "20% Hydrogen blend ready" Continuous

www.rinnai-uk.co.uk

they have internal and external models...you can fit them outside...yeah, crazy I know..

 

[Cleph]

Thanks again for your thoughts, appreciated.

Pages 4 and 5 appear to show the wiring for using SL2 on the Logic. The guide doesn't specifically say it covers Logic 2. But what is the point of having a weather compensation connector on Logic 2 if it can't do PDHW? The flyer for Logic Heat 2 definitely says that it does weather compensation. And anyway, why would a frostat need a separate switched live. It's all very strange but it could just be a mistake. I have found quite a lot of mistakes in various installation manuals. The wiring itself looks quite different to the Vogue wiring.

Yes, Vogue and Logic Max Heat 2 seem different. In summary, the Logic Max Heat 2 offers terminals: SL1 (primary on/off from room stat), SL2 (Frost Stat), OpenTherm and Weather Compensation.

The best way to get the information from Ideal might be to ask them how to do weather compensation on your boiler.

https://idealheating.com/uploads/documents/Weather_Compensation_Kit_User_Guide.pdf

Useful link, thanks, and it shows that the weather compensation is connected into the two terminals just to the right of the OpenTherm terminals in the boiler. The description in that link shows that it affects the boiler target flow temperature, but when OpenTherm is active that is what sets the boiler target flow temperature, so I am doubtful that weather compensation is the way to go.

So, did EPH advise how best to make it work? Is the relay method you currently have the official way of doing this? I also thought it would be less clunky!

EPH advised that the Influence setting in the EPH controls can be used to affect the boiler modulation and thus the temperature. But it doesn't do that with my Ideal boiler, which is very good at producing the flow temperature that is requested by the EPH control. EPH said that "It generally works well" but apparently not with my boiler.
As for the relay method, this is not an official recommendation, so I'm not overly keen on it, hence the original post asking for any better ways. However, it is just shorting the OpenTherm terminals and so is in line with the OpenTherm spec (it simulates a heat demand as from an on/off system) and the Ideal installation instructions (which show the OpenTherm connections shorted when not using OpenTherm).

 

[Mister Banks]

If weather compensation sets the flow temp and opentherm also sets the flow temp then why use both? Surely they conflict.

 

[Cleph]

https://www.rinnai-uk.co.uk/product...ted-gas-fired-commercial-water-heater-w1600in is the commercial side. I use the domestic model as I also have a rinnai combi that provides for another shower

Hydrogen and BioLPG ready condensing water heaters

The condensing N Series 30% Hydrogen blend ready continuous flow water Heaters utilise market leading patented technology to deliver cutting edge efficiencies and performance. Stainless-Steel Primary

www.rinnai-uk.co.uk

Rinnai BioLPG and Hydrogen blend ready water heaters

Rinnai Gas Multi-Point 17i Low NOx Internal Water Heater Revolutionise and go continuous flow with Rinnai high efficiency Low NOx multipoint water heaters. "20% Hydrogen blend ready" Continuous

www.rinnai-uk.co.uk

they have internal and external models...you can fit them outside...yeah, crazy I know..

There does not appear to be any mention of OpenTherm or PDHW on their website, so I don't see how your comment is relevant to my original post - please could you explain where OpenTherm and PDHW come into your recommendation?

 

[MNW67]

If weather compensation sets the flow temp and opentherm also sets the flow temp then why use both? Surely they conflict.

The point was that @Notch7 above suggested using the built in weather compensation function, as an alternative to OpenTherm, in order to achieve PDHW. The OP (@Cleph) said that the boiler isn't capable of doing that because the SL2 on this boiler doesn't allow it. I was pointing out that it must possible. It is even mentioned in the user guide (see below). Presumably the wiring would have to change.

 

[Notch7]

If weather compensation sets the flow temp and opentherm also sets the flow temp then why use both? Surely they conflict.

Weather compensation on its own doesn’t set room temperature, so that has to be done with a room stat.

My guess is to avoid cycling due to hysteresis of a standard thermostat there should be a smart thermostat which smooths the cycling, but I don’t know how that could work in practice…because as you say weather compmand opentherm would be likely to conflict each other.

I’d be interested to know as my setup suffers a bit of cycling