Viessmann Vitodens 200-W, Honeywell Rondostat HR20E

Tristar · 24 Feb 2009

I have recently had a Vitodens 200-W system boiler fitted, which has very little useful programming facility in its controller. I have no room stat and no way of programming a timed reduced room temp on the boiler - other than the very crude settings available for an overnight temp - and I would like to fit some digital radiator valve controls to make up for the programming deficiencies.
I could fit the Honeywell CM70 setup, but this costs about £500 plus fitting, so I have sourced some standalone Honeywell Rondostat HR 20E valve heads in Germany, with digital time and temp control, I can get 6 for about £200, and they would do my lounge and bedroom rads, which is where we need timed control. Honeywell say that they are not approved for use in the UK as they do not have a boiler interlock as required by building regs. However, having only 6 out of 20 rads fitted with timer switched valves would have little effect on the boiler. After all, it is only the same as me switching them off manually. I would hope that if I have one rad elsewhere fitted with ordinary locksield valves, or fit a bypass, this should be sufficient. The boiler literature suggests that only the combi version of this boiler is fitted with an internal bypass.

Can anyone advise as to any other problem with fitting these valves? Incidentally, it seems strange that you can buy these valves for use in Germany, home of Viessmann!

This boiler is very efficient, but is basically designed to give constant temp in the house all day, which I suspect very few people require. It is also unable to heat CH and HW simultaneously, and HW always has priority. It has several fancy facilities on the programmer, most of which are of little use. If you wish to have a boiler with full control of time and temps, I would not recommend this model, efficiency and build quality notwithstanding. I suspect that if Viessmann wish to sell well in the future, they will have to offer proper temp and timing controls.

Thanks

simond · 25 Feb 2009

As you may have noticed in previous postings, I import the HR20E for my installation customers.

There is no reason why you could not fit them anywhere you would fit ordinary TRVs, whatever the boiler.

Viessmann 200W can be piped up as a heat only boiler, this is the way we tend to do them because it avoids using the Viessmann controls. I don't think the Viessmann controls are bad, its just that Honeywell make them easier to use. In some situtations the Viessmann controls will give a better performance though.

Most indigenous German system boilers run HW as priority, Worcester Junkers and Vaillants are sold configured this way in Germany, but their UK derivatives are a different spec. With Viessmann you get the German model.

If a boiler is going to function correctly with weather compensation it has to know when it is in HW mode versus CH.

If you fit the remote Vitotrol 300 controller and the WC controller in your Viessmann you will get timed temperature control, in the Viessmann way.

If you want to use your boiler in the UK way, get your installer to repipe the boiler as a two pipe instead of a four pipe, fit some external motorised valves and controls.

As always, its best to use an installer who understands what he is doing.....

Tristar · 25 Feb 2009

Thanks Simon for your informative reply. You asked me last year for the link to these HR20 valves which I posted for you, but didn't know if you got the post. However you have got them now!

I realise that I could have retained my old Y pipe setup, but wished to take advantage of the increased efficiency of the 4 pipe setup with WC.

I would at least have liked the option to run CH on its own.

I was offered the 300 controller, but this is another extra cost, and, frankly, the HR20 valves offer even more flexibility. Strange that Honeywell advise against their use as being against building regs as they have no boiler interlock. My answer to that is," So what?" The existing TRVs can just as easily shutoff the flow as a timed valve.

My installer was very informative and gave me all the options, but I chose the boiler based, mainly, on good reports on this site, and the 4 pipe setup I have was my choice, but my comment about the Viessmann controls being lacking in flexibility stands. At present I have turn either the boiler temp control or TRV's up and down every AM/PM to achieve the required temp both morning/day/evening, requirements for which all vary, as I am sure is the case with the majority of users.

The party mode, economy mode and holiday settings on the boiler control are all pretty superfluous, and it would have been far more use to have had a proper timed temp facility.

Thanks again for your advice, I shall go ahead with fitting these HR20s. I don't suppose you have managed to get them with the readout the other way up have you? All my valves are mounted vertically, so I shall have to stand on my head to set them! Do you generally fit them with this type of boiler?

sus · 25 Feb 2009

why did you not zone the system and why not weather comp?

Agile · 26 Feb 2009

Yes, I was also wondering why you dont have any existing zoning if you have 20 rads!

A simple room stat creates a "boiler interlock".

Whilst weather compensation is a very useful addition to a system, many of the systems I see advertised don't bother to consider the indoor temperature.

At times of rapidly changing temperatures, sunrise and sunset for example, its important that the system takes into account both the indoor and outdoor temperatures.

Germans are much more happy to spend money on efficient new heating systems than the dull UK people. The cylinder rapidly heats in say 10-15 minutes. During that time the temperature of the fabric of the well insulated building hardly varies. In that senario its not surprising that a HW only heat cycle is more efficient and can enable the boiler to operate most efficiently whatever its current function is.

Tony Glazier

simond · 26 Feb 2009

We have also experimented with the HR40 which uses a similar casing to the HR80 but appears to have the guts of the HR20 and has the display the right way up for UK radiator fitment.

The HR20 is a unit badged as Honeywell but is made under license by another company. So far our customers have been delighted with them.

And I am sorry, you did point me in the direction of RondoStat!

Tristar · 26 Feb 2009

Agile";p="1152435 said:
Yes, I was also wondering why you dont have any existing zoning if you have 20 rads!

When the house was originally extended twenty years ago, I, foolishly, allowed the builder to design the extended pipework, so he just went for the easiest option.

Tristar · 26 Feb 2009

Agile said:
Yes, I was also wondering why you dont have any existing zoning if you have 20 rads!

A simple room stat creates a "boiler interlock".

Whilst weather compensation is a very useful addition to a system, many of the systems I see advertised don't bother to consider the indoor temperature.

At times of rapidly changing temperatures, sunrise and sunset for example, its important that the system takes into account both the indoor and outdoor temperatures.

Germans are much more happy to spend money on efficient new heating systems than the dull UK people. The cylinder rapidly heats in say 10-15 minutes. During that time the temperature of the fabric of the well insulated building hardly varies. In that senario its not surprising that a HW only heat cycle is more efficient and can enable the boiler to operate most efficiently whatever its current function is.

Tony Glazier

Thanks Tony, points all noted, these are exactly why I went for the 4 pipe/WC setup. The Viessmann does compare inside and outside temps using flow/return differentials and the external probe. However, call me difficult, but I would still prefer a more controllable system, which fitting the timed/temp TRV heads will give me.

Tristar · 26 Feb 2009

simond said:
We have also experimented with the HR40 which uses a similar casing to the HR80 but appears to have the guts of the HR20 and has the display the right way up for UK radiator fitment.

The HR20 is a unit badged as Honeywell but is made under license by another company. So far our customers have been delighted with them.

And I am sorry, you did point me in the direction of RondoStat!

Thanks again for your help Simon, I'll have a look for the HR40.

Cheers

Agile · 26 Feb 2009

Flow/return temperatures do not give a good indication of the internal temperatures.

The only way to get an instantaneous measurement is with a sensor at the focal point of the occupation.

Whilst WC can give very exact control in a static situation, switch on your big TV and you are adding say 1/2 kW of additional heating to the inside and another 1/3 with the computer. The external weather compensation does not know anything about the heat being dissipated inside.

There is apparently one controller which measures the temperature at the controller in the boiler, when its fitted in a garage?

Tony

Tristar · 26 Feb 2009

Agile said:
Flow/return temperatures do not give a good indication of the internal temperatures.

The only way to get an instantaneous measurement is with a sensor at the focal point of the occupation.

Tony

Which is why I am going to fit the HR20's in the lounge and bedroom/en-suite, both of which have 3 rads each, these being the areas in the house which require localised timed temperature control.

Thanks Tony.

Agile · 26 Feb 2009

Being a simple person who likes simple engineering solutions, I would be fitting a simple timed thermostat and a motorised valve to control the rads in each of those two rooms.

The cost would be lower and I would be using simple readily available components!

Tony

Tristar · 26 Feb 2009

Agile said:
Being a simple person who likes simple engineering solutions, I would be fitting a simple timed thermostat and a motorised valve to control the rads in each of those two rooms.

The cost would be lower and I would be using simple readily available components!

Tony

But how would one thermostat set different temperatures for different times of day in each area? Also the purchase and fitting of motorised valves would not be cheap. I can fit the 6 Rondostats for about £220 total.

Agile · 26 Feb 2009

Tristar said:
But how would one thermostat set different temperatures for different times of day in each area? Also the purchase and fitting of motorised valves would not be cheap. I can fit the 6 Rondostats for about £220 total.

There would be a programmable thermostat controlling a motorised valve in each area. Where you have three rads in each area thats the cheapest solution as well as using standard components.

Using the very cheapest components it could be as low as £40 per area for the hardware.

The Rondostats are cheaper when its only a one rad area to be controlled.

Tony

Tristar · 26 Feb 2009

There would be a programmable thermostat controlling a motorised valve in each area. Where you have three rads in each area thats the cheapest solution as well as using standard components.

Using the very cheapest components it could be as low as £40 per area for the hardware.

The Rondostats are cheaper when its only a one rad area to be controlled.

Tony[/quote]

As an engineer myself, I also search for the simplest solution to any problem, but where would the motorised valves be fitted? In my case the lounge has two rads fed directly from the boiler - which is in a utilty room - under a screed floor, the other rad is fed from a supply upstairs down ducting and again under screed.

The bedroom has two rads from one underfloor supply, the en-suite from another, because the bedroom is in an extension, and the ensuite was a bedroom in the original stucture. I think I would have to have at least 4 motorised valves, plus two thermostats, and associated wiring, and finding a suitable fitting point for each item would be challenging, to say the least, particularly as they would have to be easily accessible. Also, I prefer to fit good quality components, which are usually not the cheapest.

Also I have got the decor in my house in fairly good order, and have no wish to disturb it unnecessasarily.

Cheers

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Viessmann Vitodens 200-W, Honeywell Rondostat HR20E

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