Control Options

[D_Hailsham]

I now have a new Avanta 18S that since it's installation I've been using with a CM927. Earlier this week I finally received a iSense RF from Holland and I've spent a few nights this week temporarily hooking it up and seeing what it does.

Do you have a mid-position valve? If so, it has to be converted to a diverter and turned round, so Port A is to the HW and Port B to the Heating (see Options 6 and 10 in the Suggested Schematics book).

The reason for this is that, in heating mode, the boiler temperature is controlled by the outside sensor, so it could be anything from 30C to 70C. This means it may not be hot enough to heat the cylinder. The system therefore automatically raises the flow temperature to maximum and stops circulation through the rads.

If it's of any use, here is a table showing the temperature/resistance values for a red-band sensor (right hand column). There is an obvious typing error as 20degC should obviously be 14770, not 1477.

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• D_Hailsham
• 29 Jan 2011
• 1

The iSense Installation Manual says:

Tap water temperature
1. Select Menu > Settings > DHW > DHW temp.
2. Select one of the following options:
- Temperature: select the temperature that the hot tap water must have continuously.
- Clock program: use a clock program to determine the temperature of the tap water. Setting this clock program is virtually identical to setting a clock program for the desired room temperature.

This is described in paragraph 5.1.

The maximum temperature that can be set depends on the boiler settings.

When setting a clock program, start this an hour before you first require hot water. This gives the boiler sufficient time to heat up

 

[dumbrill]

I've only been testing out the iSense for an hour or two at a time and then switching back to my CM927. At the moment the boiler is controlled by a simple 230V coming from the wiring centre and this switches the boiler on via terminal 1 of X2, ie. CH mode. This is a simple temporary solution for a few weeks until a new unvented cylinder gets fitted next to the boiler. At the the moment the flow control is via the original three way valve that is located up with the soon to be removed hot water cylinder. The new diverter valve is plumbed in on the boiler outlet, but just sitting in it's denergised position flowing AB to B. The new pipes to and from the soon to be installed cylinder are capped off. None of that though is really relevant.

For testing I have removed the live into X2 and setup the system for the iSense. That is

terminals 1 and 3 linked to 4 on X2
the iSense across terminals 7 and 8 of X9
the WC sensor located outside and connected across terminals 1 and 2 of X9 and
a red band sensor for HW connected across terminals 3 and 4 of X9
a spare motorised valve connected across terminals 1 and 2 of X5.

With the above, the system works as it should. I can see it coming on in either CH of HW mode (3 or 4). The motorised valve works OK. CH controls to a room temperature OK. I can get outside and HW temperatures reported on the boiler and iSense. Weather compensation appears to work OK, but it's not been on long enough to really test out.

I haven't yet though got the HW control working OK. My first test was with a simple on/off switch across terminals 3 and 4 of X9 to simulate a cylinder stat. The problem I had was that whatever time was set on the iSense it would still fire up the HW when called for.

Last night I set up the system with a thermistor across terminals 3 and 4 and it wouldn't control to a temperature. I was using a hairdryer to heat it up the sensor and whilst it reported a seemingly correct temperature the boiler didn't cut off at the set 60 degC.

Have you had any success in using a sensor for HW? Does the iSense normally control HW to a time programme using either a cylinder stat of sensor?

Thanks for the resistance table. I've checked the resistance of the HW sensor at room temperature and it matches the figure in your table. I'm reasonably confident that a red band outside sensor is the same as a red band HW sensor (just different packaging).

 

[D_Hailsham]

The new diverter valve is plumbed in on the boiler outlet, but just sitting in it's de-energised position flowing AB to B. The new pipes to and from the soon to be installed cylinder are capped off.

Is the new diverter is the correct way round - B to heating , A to cylinder?

I can see it coming on in either CH or HW mode (3 or 4).

Not sure what you mean by 3 or 4.

The motorised valve works OK. CH controls to a room temperature OK. I can get outside and HW temperatures reported on the boiler and iSense. Weather compensation appears to work OK, but it's not been on long enough to really test out.

Are you talking about the original 3-port valve?

I haven't yet though got the HW control working OK. My first test was with a simple on/off switch across terminals 3 and 4 of X9 to simulate a cylinder stat. The problem I had was that whatever time was set on the iSense it would still fire up the HW when called for.

Last night I set up the system with a thermistor across terminals 3 and 4 and it wouldn't control to a temperature. I was using a hairdryer to heat it up the sensor and whilst it reported a seemingly correct temperature the boiler didn't cut off at the set 60 degC.

Is this with the original 3-port or the new diverter valve?

I'm reasonably confident that a red band outside sensor is the same as a red band HW sensor (just different packaging).

That's what I think. The table only mentions red band, no distinction for outside or cylinder.

 

[dumbrill]

Not sure what you mean by 3 or 4.

3 or 4 refers to the the codes displayed on the front of the boiler; 3 for CH and 4 for HW.

On the basis that a picture tells a thousand words then hopefully the attached diagram makes sense of my earlier post.

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• dumbrill
• 30 Jan 2011
• 1

[/img]

 

[D_Hailsham]

On the basis that a picture tells a thousand words then hopefully the attached diagram makes sense of my earlier post.

That helps - raise more questions.

But I'll wait for you to tell us what caused the problem.

 

[dumbrill]

On the basis that a picture tells a thousand words then hopefully the attached diagram makes sense of my earlier post.

That helps - raise more questions.

But I'll wait for you to tell us what caused the problem.

OK, but the same two questions:

Does a HW thermistor normally control the HW function OK with the Avanta and/or iSense?

and

Does a non-RF iSense control HW to a time programme using either a cylinder stat or sensor?

I would like to know if i'm wasting my time trying get what I've got working.

 

[dumbrill]

Success at last!

I rigged up the iSense yesterday and again this evening and substituted a potentiometer for the DHW sensor and got some predictable results.

The key was switching off the Legionella Protection on setting P25. With this 'off' the DHW will control around the set point input into P2. With Legionella Protection 'on' the set point is 65 degC which is no good for day to day use.

The only thing the iSense won't do is control either the DHW on/off times or temperature. So a separate timer is still required and temp has to be set on the boiler. I don't know whether this is the same for a wired iSense/Avanta combination?

Using the red band figures I've managed to buy thermistors that exactly match the required values. With a bit of careful packaging for protection one of these will still be small enough to fit into one of the sensor pockets on the tank alongside the other stats. This then leaves me with control via the sensor and the boiler opening both the diverter valve and the primary coil isolation valve via X5 when DHW is required.

 

[dumbrill]

Or you could buy a Viessmann Vitodens 200-W System boiler with weather compensation and a cylinder temperature sensor - and just fit it straight out of the box.

You can add mixers for two underfloor circuits as well, the boiler can control all four circuits plus solar.

I'm not going to disagree .....

 

[mehran]

since you work for viessmann mysteryman, That is advertisement

anyway, intergas is better...

 

[dumbrill]

Well it's up and running now with the new cylinder and it works as expected with the added bonus of also controlling the DHW as well. This didn't seem the case when I tested it before, but now as installed and having been running for a few days, it does limit the water temp according to the clock programme for hot water. This overrides the HW temp setting in P2 of the boiler.

Overall its easy to use and I'd recommend it. I don't know why Broag Remeha don't package the RF version, a DHW sensor and a WC sensor up in a kit with some better instructions and educate their helpdesk a bit. Then they would have something equivalent to the Vaillant or Viessman offerings.