Worcester Bosch CDi Programmer

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Hi Again,

I was meant to be having a WB 37 CDi installed this week but fitting has been delayed a week or so. Sorry to bang on about my own system but I feel it’s best to gather information before fitting if possible.

My question (still) revolves around the dilemma of fitting a Worcester Bosch DT10RF Optimiser or a Honeywell programmer (CM927 or Sundial RF2 pack 2); I understand I might still need to get wiring advice from Worcester Bosch if I go for the Sundial.

My concern is to do with the “Cycle Rate” on either of the Honeywells; this does not appear to be a parameter offered on the Worcester Bosch programmer. As the 37 CDi modulates the heating within the boiler itself, doesn’t that make “cycles per hour” controlled by the programmer as counterproductive (obsolete)? If this is not the case then, then does this mean that the DT10RF is an inferior controller for heating?

I suppose what I’m trying to discover is if the Honeywell programmers are better suited to a previous generation of boilers or, if the Worcester Bosch claim of “fully modulating” is not really doing anything for me?

Thanks Again,
soup
 
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My concern is to do with the “Cycle Rate” on either of the Honeywells; this does not appear to be a parameter offered on the Worcester Bosch programmer. As the 37 CDi modulates the heating within the boiler itself, doesn’t that make “cycles per hour” controlled by the programmer as counterproductive (obsolete)?
The Honeywell devices are trying to do a different thing to the boiler modulator.

The modulator controls the boiler output to maintain the required water temperature; the Honeywell prevents overshoot.

On a traditional system with mechanical thermostat, the boiler runs until the thermostat reaches temperature and turns the boiler off. Unfortunately the radiators continue giving off heat and the room gets too warm. The immediate reaction is to turn the thermostat down a degree or two. Unfortunately the difference between on and off temperatures on this type of stat can be as much as 3 degrees. The result is that the room temperature actually drops maybe 5 degrees before the boiler turns on. Result, everyone feels cold. So the thermostat is turned up again and the vicious cycle starts again.

The Honeywell thermostat runs the boiler continuously until the room temperature is 1.5 degrees below the required level. It then starts cycling the boiler on and off. The length of an on-off cycle is determined by the number of cycles per hour. If is is set to six, the cycle length is 10 minutes. During that ten minute period, the amount of time the boiler is ON will depend on how far away the actual temperature boiler from the required temperature. If it is 1.5 degrees below it will be on 100% of the ten minute cycle at 1 degree below it will be on 66% of the ten minutes at 0.5 degrees below it will be on 33% of the ten minutes.

Controlling the boiler this way means that there is no overshoot and room temperatures are virtually constant.

There is another setting, which is the minimum time on, usually left at one minute. You can also increase the temperature difference (normally 1.5 deg) at which the programmer starts cycling.

I suppose what I’m trying to discover is if the Honeywell programmers are better suited to a previous generation of boilers or, if the Worcester Bosch claim of “fully modulating” is not really doing anything for me?
The modulator certainly works by adjusting the boiler output to keep the water temperature at the set value. However it is possible to do more with the modulator. The required water temperature varies with the outside temperature (cold=high temp, warmer=lower temp). The water temperature can be controlled by modulating the boiler.

This is called Weather Compensation and WB's version is the FW100, which is compatible with your boiler.

green=edited
 
The on-off "modulation" of the Honeywell controller may not be completely effective on a powerful combi boiler like the 37CDi. Even with a relatively short on period, the boiler may be able to maintain a fairly high flow temperature and you will still overshoot your desired temperature. Details will depend on the boiler's own modulation program and how it reacts to the set and actual temperatures when the controller kicks it back on.

The load compensation of the FR10 controller "simply" turns down the flow temperature as the room approaches the setpoint, and leaves the boiler to work out how to achieve that. The boiler may well still have to switch on and off to maintain a low flow temperature, and the details can be controlled from the boiler menu. Another benefit of the FR10 method of control is that the pump continues to run throughout the period of heat demand, while it will switch on and off as the Honeywell controller cycles (depending on the pump overrun period).

I don't believe that the DT10RF optimiser performs load balancing (flow temperature adjustment), so all this may not matter to you.
 
Thanks for your explanations, I see how the two functions have different tasks to perform.

I don't believe that the DT10RF optimiser performs load balancing (flow temperature adjustment), so all this may not matter to you.

It also appears that the DT10RF does hot cycle either, so compared to the Honeywell controllers that do...

If this is not the case then, then does this mean that the DT10RF is an inferior controller for heating?

I am now making that assumption, do you feel I’m justified in that statement?

Thanks,
soup
 
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It seems to be common that the wireless controllers have less functionality. I'm not sure why this should be other than meeting some arbitrary price point.

does this mean that the DT10RF is an inferior controller for heating?
I'm not sure I'd choose the word inferior, but certainly if you want some form of modulation from the controller then this wireless one isn't the one to choose. To clarify, the FR10 itself could be considered inferior because it does not allow different setpoint temperatures to be programmed at different times of the day. In fact it doesn't recognise the time in any way and normally would be used in conjunction with a separate timeclock. In that respect it could be considered inferior to the DT10RF. WB offers other compensating controllers with more functions.

What a pain, eh? Best to investigate now rather than end up with the wrong controller.
 
Your really better off with the DT10RF with the 37CDI combi rather than the Honeywell, which I have in my own house, for two reasons.

The DT10RF comes with the same warranty as the boiler which is five years if a WBAI installs the boiler and the DT10RF controls the boiler hot water pre-heat whereas the Honeywell can't do this.

Cost wise your talking £170 for the DT10RF which is basically two programmers and five years warranty or the Honeywell (better programmer IMO) at £100 with one year warranty.

Tony
 
Thanks again for all your feedback, especially ianniann who has been offering me lots of balanced advice.

I’d like it if my plumber can fit me the Honeywell Sundial RF Pack 2 (Y9420H), this will give me two channels so I can have hot water preheat, it will cycle the boiler and, the thermostat is portable.

In previous threads, folks have indicated that the 37 CDi can’t be wired to a two channel controller unless it’s a Worcester Bosch controller. I have phoned WB three times, including today, and each time they are adamant that any 240V two channel controller can be fitted to the 37 CDi and work correctly. As advised, I asked how this is done because the 37 CDi connecter (ST10) only has three terminals and the descriptions suggest they are all for the thermostat and not the preheat;

Thermostat LIVE (Ls)
Thermostat LIVE return (Lr)
Thermostat Neutral (Ns)

The WB engineer said that the Honeywell could be connected to these and the pre heat would be controlled by the timer.

I feel wrong challenging the information given by the WB engineers (I’m just a consumer) but two different posters flagged that they might not be compatible; can someone confirm if the Sundial RF Pack 2 would control the preheat using as those connections?

Many Thanks Again,
soup
 
If your having a WB 37 CDI combi boiler installed mate then to control that boiler's pre-heat facility you have to use a WB programmer because the receiving unit for those programmers plugs straight into the boiler's PCB and this receiving unit is in effect the hot water preheat programmer.

When your fitting these WB programmers you remove the blank facia on the control panel and slot in the recieving unit after plugging it into the socket on the PCB.[/i][/b]
 
The WB engineer said that the Honeywell could be connected to these and the pre heat would be controlled by the timer.
The three standard terminals you described only control the central heating function. It is hard to imagine any way that these terminals could also control the pre-heat and certainly the documentation does not describe anything. I can only imagine that whoever you are speaking to is not understanding your question. Ignoring the live (Ls) and neutral (Ns) which obviously don't control anything, there is one terminal (Lr, live return) that is switched by the controller to demand heat. Ask them to explain how this also controls the pre-heat.

I guarantee that applying 240V to Lr on a 37CDi demands central heating but does not affect the DHW pre-heat function in any way. The way that the pre-heat function is switched on and off by the WB controllers is by the connections behind the facia plate and I have no clue how these would need to be wired to a third party controller.
 
Thanks again, I’m not happy with the information I’m getting from Worcester Bosch, that’s why I’m not letting go.

I believe the engineers understand the functionality of their own DT10RF controller and, that they understand my question otherwise they wouldn’t be advising me that I need a two channel controller.

I feel they must be lacking in knowledge of connecting a controller to a CDi though this does seem strange to me.

I have now contacted them in writing, explaining the situation and expressing that I believe connecting to Lr will not control the preheat function (thanks ianniann).

soup
 
I think this is just a matter of Worcester Bosch admitting that only their own controllers can do both channels.

The choice for me (and everybody) will be:

1) If you want to control hot water preheat times then you have to fit their own controller.
2) If you want a controller that cycles the boiler and does not have to be wall mounted and has a number of optimising options, then you won’t get the timed preheat control.

I think that’ll be a pretty poor show, surely it wouldn’t have taken much to add a connection to allow third party controllers to connect to the preheat channel?

soup
 
You can always have the Honeywell programmer or another programmer and simply leave the pre-heat on or off, personally I think the WB programmers are a no brainer option for the reasons already mentioned.

The pre-heat feature is really only a 'convenience' feature anyway mate, these CDI combis provide excellent hot water, the pre-heat is just a nice 'extra'.

Some of my customers just turn it off even if they have a DT10RF Optomiser, some of them even turn off the optimising feature on the programmer too.

These programmers are just rebadged Draytons/Danfoss (can't remember which) anyway with the addition of the boiler fascia module.
 
At last... the Worcester Bosch technicians confirm that you can’t connect a working, third party, two channel programmer!

Dear Mr SOUP

Thank you for your enquiry.

If you were to use a third party programmer then the only influence you would have on the boiler would be for the heating circuit and you would not be able to control the hot water pre heat function.

Kind Regards

Technical Support
Worcester Bosch Group
 
Hi Again,

At the very start of all this advice I’ve been seeking over a number of weeks, I asked the question “can the 37 CDi be wired to a CMT927 receiver and another timer to control the hot water preheat?” specifically the Worcester Bosch DT20. I got the answer that this was not possible. Maybe my question wasn't as clear as it could have been.

//www.diynot.com/forums/viewtopic.php?t=225139

When I rang WB technical advice, they also said this can’t be done and sent me down the incorrect “two channel programmer” route / debate.

Today I have emailed Worcester Bosch asking the same question, fit a DT20 to the boiler and a third party controller to ST10. Here’s their answer:

Dear Mr SOUP

Thank you for your enquiry.

To do what you want you would need to set the heating on the DT20 permanently on then use the Honeywell programmable room thermostat to control the heating. The DT20 can then be used to control just the hot water function. Alternatively you could use our DT10 RF optimiser.

Kind regards
Technical Support
Worcester, Bosch Group

Short answer, you can connect two controllers to a 37 CDi boiler (please check with Worcester Bosch yourself before making any commitment).

This solves all my problems and gives me the best of both worlds.

Cost wise, a DT20 and a CMT927 come in at a similar price to the DT10 RF optimiser.

Thanks for helping me thrash this out with Worcester Bosch.

soup
 
But the Honeywell CM927 will only have one year's warranty whereas the DT10 RF and all WB controllers have the same warranty as the boiler which is an additional four years if installed by a WB AI.

IMO the Honeywell is by far the better programmer but I've had a couple go toes up just out of warranty and also some of the DT10RFs have gone the same way but those haven't cost my customers a bean except for the inconvenience which would have happened in either case.

Tony
 

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