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Discuss Viessmann 200-W Combi 35kw (New 2019 version) Installed - Advice? in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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Evening All,

Hoping some plumbing/heating engineers/other knowledgable folk on here might be able to assist with some questions about my new boiler.

We had the new Viessmann 200-W 35kw Combi installed this week by a Viessmann registered local heating engineer. It's the new 2019 version with the increased 17 litre per minute DHW flow rate and the larger screen on the front. Very recently released or so I'm told. It replaced a 14 year old Vaillant Ecotec 831 Combi which was beginning to have issues. We had hoped that a newer boiler would give us better hot water flow rates and lower gas bills. Have been told by multiple people that Viessmann are the brand to go for these days.

We didn't get off the to the best start when it was installed, turned on and promptly died. Viessmann themselves had to come out 2 days later (meanwhile no heating or hot water - not brill with 2 young kids) and replaced 3 internal boards including the front panel. Problem solved, but with it being a brand new model there was lots of head scratching and phone calls back to technical department.

It's wired into our existing Honeywell Evohome system which has 12 zones with all radiators on the wireless TRV's. We have a towel rail in the bathroom with no TRV and that's permanently open which I think needs to be the case to allow the boiler to circulate when the TRV's close themselves off. Because of this, the boiler runs in 'continuous' mode rather than weather comp or whatever the other option are.

Seems to be working OK now, BUT:

1) We couldn't get water hotter than 41c out of the bath hot tap. Boiler set to 60 degrees. I filled a bucket and timed it, the flow was 17 litres per minute or just over but the incoming main temperature is about 11 degrees. The boiler is rated at 17l/m, but is this a certain number of degrees over the incoming temp (i.e. if that's 17l/m at a 30c raise, should this be about what we would expect?) The plumber thought that the boiler should limit hot water flow to what it is able to heat to the set temp, so either this is not the case or it's not working properly. Either way, with a screwdriver I reduced the flow into the boiler on the inlet valve underneath it until (with the bath hot tap on full and monitoring the boiler display) the set temp could be met (we get 10-11l/m now at 60 degrees so a small improvement on the previous boiler which I measured at 9.1l/m before it went). I had hoped for better, but couldn't find a graph/table anywhere showing what litres per minute should be achievable at a particular incoming mains water temp?

2) Seems to take much longer than the old boiler to start producing hot water. We seem to have to drain off quite a bit now before it runs hot, this was not the case before so the pipe run shouldn't have anything to do with it (and it was a straight swap). I notice the heating settings on the boiler have "Normal Flow" and "Reduced Flow". I assume normal flow is the temperature of the boiler when the heating is on, and reduce when there is no heat being called for. These were 70 degrees and 20 degrees respectively. Would increasing the reduced flow temperature likely have any bearing on the speed of DHW production? The boiler seems to ramp up fairly slowly - it sounds like a jet engine being throttled up gradually! I can't see any mention of an 'eco' mode or anything either.

Many thanks in advance for any thoughts on the above!

ST.
 
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ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
is the bath thermostatically controlled, easy way to tell what flow rate do you get out of your other taps and are the hot , also the temp is effected by pipe cooling are you pipes insulated eg under the floor ect as you will loose a bit if there not (around 5dc)

as for the hot water taking along time this will be the same as your old boiler but the only difference is were you using the pre heat function on the vaillant ?
 

scott_d

Plumber
Gas Engineer
Most 40kw combis will give 16lpm at a 35 degrees rise.
So 17lpm at 30 rise sounds about right.

Is there a pre heat/comfort function for hot water?
 
is the bath thermostatically controlled, easy way to tell what flow rate do you get out of your other taps and are the hot , also the temp is effected by pipe cooling are you pipes insulated eg under the floor ect as you will loose a bit if there not (around 5dc)

as for the hot water taking along time this will be the same as your old boiler but the only difference is were you using the pre heat function on the vaillant ?
Thanks for the reply -

No the bath isn't thermostatically controlled it's just a mixer. It's got the best flow rate of the taps in our house, but that could be as it's directly above the boiler? The boiler has a screen you can pull up (and also shows in the iPhone app) that shows what temperature the boiler is able to heat water to as it passes through.

I'm afraid I have no idea if the pipes are insulated, but all the plumbing is on one side of the house so nothing has to go very far. I'll assume they aren't insulated!

I wasn't aware the Vaillant had a Pre-Heat function... It was the boiler we inherited with the house when we bought it, and left it to do its thing... It heated water very quickly though so perhaps it was on? Does the Viessmann have a similar function?

The boiler manual talks about enabling the circulation pump to provide faster hot water to the taps, but I assume this is not applicable to a combi?
 

Brambles

Advent Win
There are at least two main version types of the 200W and they are very different. From your post it reads as if there may be now a third version that I have not encountered.

The WB2B is fairly straightforward and the 35kw combi should deliver around a 35 degree temperature rise at 14 to 15 litres/minute if set up correctly with a consistent cold water inlet pressure of at least 15 litres/minute. As expected DHW, when called, takes priority over heating. As with all Combi’s, test and configure it against the closest unrestrained hot tap.

The B2HB / B2KB is (I think the same heat exchanger) but (in my view) overly complicated with included options for solar heating, underfloor heating, dhw storage combined with combi operation et al. The combi DHW output is around 3 litres / minute higher, but at 30 degree delta against the to WB2B, but it must be set up correctly to achieve this - which is not the quick and straightforward process that you would expect. This version has to be specifically configured for Combi DHW to take priority over all the other heating options. To set this boiler up properly you need a heating engineer who is either very familiar with this type of boiler or one who has done his / her homework on the commissioning sequencing before arriving at your property.

With respect to your comment on weather compensation, there is no reason why that should have been disabled and set at “constant temperature” from the installation you described. On the 200W ( both versions) - weather compensation is the standard configuration. That is possibly an indication that whoever commissioned the system was not completely up to speed with the control configuration process.
 

EvilDrPorkChop

Gas Engineer
Advent Win
There are at least two main version types of the 200W and they are very different. From your post it reads as if there may be now a third version that I have not encountered.

The WB2B is fairly straightforward and the 35kw combi should deliver around a 35 degree temperature rise at 14 to 15 litres/minute if set up correctly with a consistent cold water inlet pressure of at least 15 litres/minute. As expected DHW, when called, takes priority over heating. As with all Combi’s, test and configure it against the closest unrestrained hot tap.

The B2HB / B2KB is (I think the same heat exchanger) but (in my view) overly complicated with included options for solar heating, underfloor heating, dhw storage combined with combi operation et al. The combi DHW output is around 3 litres / minute higher, but at 30 degree delta against the to WB2B, but it must be set up correctly to achieve this - which is not the quick and straightforward process that you would expect. This version has to be specifically configured for Combi DHW to take priority over all the other heating options. To set this boiler up properly you need a heating engineer who is either very familiar with this type of boiler or one who has done his / her homework on the commissioning sequencing before arriving at your property.

With respect to your comment on weather compensation, there is no reason why that should have been disabled and set at “constant temperature” from the installation you described. On the 200W ( both versions) - weather compensation is the standard configuration. That is possibly an indication that whoever commissioned the system was not completely up to speed with the control configuration process.
I think their point was as they've got EvoHome it wouldn't work well with the Weather Compensation as your variation in flow temperatures you would experience wouldn't work well with EvoHomes learning algorithm, they really needed to use OpenTherm. However as i'm unfamiliar with the Viessman combis i'm not sure this is achievable as i've only ever done it once with a Heat Only Viessman.

OP - The temperature rise seems about correct, you either balance it down like you have done or live with the 41oc coming out the bath tap and open the tap accordingly. You have to bear in mind that a 41oc bath is pretty hot..
 
Photo attached of boiler, if it helps. It's only been out a few weeks I believe. Larger front screen than the previous model and no physical buttons. Nightrider style light bar above the panel. Looks cool. Shame it's going to be built into a cupboard after the carpenter is finished!

IMG_9992.JPG

OK so the thoughts here are that the DHW flow is about what we would expect for the temp of the incoming mains water. 41 is absolutely fine for a bath, but the manual says that the temperature should be 50 degrees or more for hygiene reasons.

Are there any settings in the boiler that would allow faster production of hot water?

What is Opentherm, should I be using this now with the new boiler? Is there something I need to add to my Evohome setup to run the boiler more efficiently?

Here are both ends of my Evohome setup...

IMG_9993.JPG

IMG_9994.JPG

Thanks again.
Post automatically merged:

(As for the model number my user manual says B2HE, B2KE)
 

EvilDrPorkChop

Gas Engineer
Advent Win
Opentherm is a Protocol which allows the controls to tell the boiler what Flow temperature it requires. Using Opentherm with EvoHome would allow the Evohome to tell the boiler what flow temperature it required to enable it to keep a room at a set temperature, or get it up to temperature. If one of the Zones current temperature is out more than 1.5oc of the set point Opentherm would then request 100% demand from the boiler. However even thought it's an open standard it does have it compatibility issues across many manufactures.

However as I said in my previous posts I'm not familiar with Viessmann and only fit Vaillants, however we do a lot of EvoHome systems.
 

townfanjon

Esteemed
Plumber
Gas Engineer
Advent Win
Yes that is the new 200 , we had the first viewing of it via the viessman van on Friday .
I haven’t read all the comments so sorry if I have missed anything but IMO , just run it 24/7 on the viessman WC not constant temp .
 

Brambles

Advent Win
From what you have described is Evohome controlling the UFH or is it operating in unconstrained operation? I would recommend that the UFH with your boiler would probably be better controlled using Vitodens add on module. It should not be left on unconstrained operation unless the full system is only Combi DHW and UFH.

The DHW temperature is adjusted through the menu function - up to 60 degrees (I think).

Pork Chops comments on Evohome with weather compensation are correct in my experience Evohome deals with the problem, provided that all other parameters are left unchanged.

I would not recommend converting to Open Therm operation until the current system is set up correctly. Your existing Evohome system can easily be configured to operate a Viessmann boiler through Open Therm, but not with the UFH in unconstrained mode
 
From what you have described is Evohome controlling the UFH or is it operating in unconstrained operation?
We don’t have any underfloor heating - it's an old Georgian house with normal rads in each room.

My understanding of how it's set up from what I can gather from the manual/screen is that the boiler is set to "Continuous operation" which means that flow temp is 70 degrees when the Evohome calls for heat (either on or off) or lower when it's not demanding heat (which from what I can worked out is the 'Reduced Flow' temperature) which was set to 20 degrees.
Post automatically merged:

Yes that is the new 200 , we had the first viewing of it via the viessman van on Friday .
I haven’t read all the comments so sorry if I have missed anything but IMO , just run it 24/7 on the viessman WC not constant temp .
The engineer as far as I am aware didn't install anything outside though as felt it unnecessary due to the Evohome?
 

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