My Viessman boiler journey

[marshian]

22 minutes ago, MrPotts said:

OK, i think its time to get someone in that can investigate how the boiler has been wired.

 

And there is my problem - I got the only Viessmann trained gas engineer for 50 mile radius to do the job - the other installer 50 miles away didn't want to quote because the distance made it not worth his while.................

 

Maybe I should ask Adam from heat geek if he fancies a boiler challenge............

[marshian]

Well time to round this out (Not quite there but damn close)

 

No mater what I did with the Wiser Hub (controller) - All Off, HW On, HW Off, CH On, CH Off or Both CH and HW On the wire from the wiser unit to the wiring centre to trigger the HW was live all the time.

 

I was completely confused by this as it shouldn't be live unless the timer is calling for HW but I checked the wiring instructions and it was all wired correctly 3 for HW and 4 for CH

 

 

I swapped to a different (spare wire) - same result 240V all the time unless the power to everything was killed

 

The CH wire is only live when the timer and the room stat is calling for heat

 

Every time I check wiring in the wiring centre or remove the Wiser Hub I switch off the power to it all at the Fused Spur that feeds it all

 

I don't know why I did what I did next but I took the Wiser hub off the universal back plate without powering down and I heard an audible click and I stopped - a penny (very large one dropped) - selecting CH or HW had always made an audible click but since the boiler install and change of wiring that had been missing for HW the light comes on but no audible click.

 

I switched off the fused spur - re-attached the Wiser hub and if I selected HW I got a audible click, CH again I got an audible click

 

Going up to the wiring centre with nothing selected on the hub I had no power to either HW or CH signal wires

 

Selecting HW gave me 240 volts and same with CH with nothing selected I got no Volts on either HW or CH

 

My only thought is that somehow the relay or contactor for HW had stuck closed and even powering down the unit was not causing it it open.

 

Anyway everything now works and just need the gas engineer to confirm with Viessmann that a switched live back to the boiler is needed (I'm damn sure it is but I'm not about to fit that)

 

I actually need to think about how the boiler gets that in summer or if heating water outside of the CH period because I can't have both CH and HW linked to the same switched live signal to the boiler or CH will drive HW

 

I might have to either

 

A. think about a relay solution

 

or

 

B. think about a switch (Summer / Winter setting) I can only have one SL wire at the boiler so for Summer the SL comes from the HW side but for winter when I only heat water during the CH timed period it can come from the CH side.

[marshian]

So Viessmann Hot water demand box throws 80 deg C at the HW coil and ramps up to 100%

 

Yes water reheat times are super quick but the boiler is quite noisy when it does HW and the tank only really can cope with 3-8 kW without the return temps being 10 deg less than the flow (Old boiler min was 10kW and that gave similar HW times to the viessmann when I ran it at 80 Deg C to get the water done without cycling)

 

So if the boiler modulates based on return temps or flow (or both)

 

 

 

 Hello gate valve - happy to have you join the party - lets shut you down a little and see what happens

 

80 Deg C flow - boiler initially hit 100% but as I closed the valve it  modulated down to 30% - 20 deg difference between flow and return (76 deg flow 56 deg return) - water heated from 20 deg to 52 deg in 22 mins

 

It was a bit shunty to start with till I found a place where the boiler wasn't overshooting ramping down and then as the flow temp dropped too much throwing much higher kW at the circuit again

 

Basically 1 turn open from closed seems to work fine - that'll do for starters

[marshian]

Well my old school plan had a flaw - it wouldn't have been a problem if the gas engineer had used my 3 port valve as I proposed with no mid position in the old airing cupboard arrangement because I only had a bypass fitted for the CH side - HW didn't need one because the flow rate was always far higher (easiest path and all that)

 

However now I have a bypass that will work if pressure in the system is high with CH or HW - closing the gate valve to increase the amount of time the water stays in the coil and reduce the return temp to the boiler is enough pressure to cause the bypass to want to play (By play I mean get involved)

 

So tonight I've been experimenting with pump parameters to see if I can find a pump setting that

 

Provides a min of 0.4 m3/Hr so that the boiler is happy with the level of flow (below 0.4 m3/hr the boiler gets a bit fussy and throws the odd "low flow" fault) when circuit is at it's smallest (ie just one or two rads in circuit)

 

And provides a max of 750 - 800 l/hr (0.8 m3/hr) when all the rads are calling for heat so the boiler can ramp up and get the circuit up to temp

 

Because the alternative plan is fit a NO zone valve in the bypass line so it closes at the same time as the CH NO zone valve...........

 

Anyway no one wants to see a load of tables of what pump results in terms of watts, head and m3/hr is like for 3 different pump operating modes each with 3 different speed settings for both all rads calling for heat and a very tight circuit where I'm left with just two rads still calling (Bypass was closed for this) so I'll just say I've found a setting that meets the requirements but I haven't done HW on it yet.

[marshian]

In other news Gas Engineer has had it confirmed from Viessmann that boiler (in current configuration) needs a switched live from the programmer to the boiler - at bloody last!!!

[marshian]

Warning long post - Bit of a catch up going on

 

Still working with the boiler to get the house heating where I want it

 

In November I was still heating to a schedule

 

Got the weather comp pretty much dialed in for that type of heating method now.

 

I've tempered the HW demand boxes appetite for throwing everything the boiler has to give at the HW tank (I've opened the the gate valve on the HW Tank return to 33% - lower than this and the boiler occasionally hunts a little as well as opening the bypass a little which you don't want on HW heating)

On weather comp a 1,4 Slope is a good compromise for scheduled heating - lower than that and the house takes a little too long to get to temp.

(especially the living room which as I've said a few times is slightly compromised - a 600 x 1400 T22 rad at one end of a 6.2m x 3.6m room was on the borderline when I did the heat loss calcs last year but I thought with less cycling and a more constant flow temp from the new boiler planned it would be OK)

Higher slope than that and it gets the house up to temp a little quicker but too many rads shut down and then the circulation flow is too low for the boiler to be happy.

Flow temps at the boiler around 8 deg C outside temp is 40 deg and return at the boiler is around 30 deg C

All the rads are running at around 6 to 7 deg drop between flow and return

I'm pretty near my target 4,00 kWh/HDD (slightly over some days when temps are a little warmer - slightly under when cooler)

On one day the boiler did one burn from 3 pm to 7.30 pm which I am really happy about but more importantly all the rooms warmed up equally - even the living room but that's nothing to do with getting the weather comp dialed it......

What the difference??

I dipped my hand in my pocket weekend before last and purchased a new rad and I fitted it back end of last week.



700 x 1400 K33 (triple panel, triple convector) Yes I know it's a smidge below the min recommended height above the floor - I'll fix that next summer (consequence of raising the floor level by 20mm when I fitted oak flooring) but it's solved the rooms issue of always being the last to get to target temp.

At the weekend Mrs BC (not known for her tolerance of cool temps) actually said can we have the heating off..............
 

In December I moved to 24/7 heating with set backs (as opposed to off with scheduled heating)

 

As a result I moved to a WC curve of 1.0 with 2 deg setbacks however Initial results were good from a Mrs BC perspective but sheesh it really didn't work well on warmer days - the house overshot temps and my kW/HDD was way over target. WC is supposed to be better than that so I was a little disappointed.

 

The other main issue was the boiler wasn't modulating down to min before shutting down (I think reduced circuit size was having an influence due to some rooms being up to temp and others still needing heat)

 

I have controls on my phone for Boiler and room temps I decided to push it a little and try 24/7 with no set backs and over the course of 5 days I reduced the curve from 1.0 to 0.6 and the slope from 4 to 0

However I know the rooms in my house that lose temp fastest and they are areas not used all the time (Study, Front hall, kitchen - all north facing) so a few areas as still on schedule the rooms used most are now pinned 24/7 on anywhere from 18 to 21 depending on room function

Anyway Flow temps at Outside Temps for the three WC curves are below
 

Outside Temp	WC 1.4	WC 1.0	WC 0.6
20	20	20	20
10	36	32	27
0	49	42	33
-10	60	51	39

So in a nutshell at 0 deg outside where I was running 49 deg C on scheduled heating slots - I moved to 24/7 with setbacks running 42 Deg C and I'm now running 33 Deg C 24/7 effectively with no set backs

The boiler runs for nice long periods at min modulation - initially I was a bit concerned that it was going to be an expensive experiment but kW/HDD is slowly shifting back towards my design target of around 4.0

Last week as we were home for Xmas I had time to experiment and set the majority of the TRV's as high limiter (ie 2 deg above the room target temp) and watched to see if rooms exceeded the target temp - a couple did so I knocked back the flow to those rooms using the EB4 TRV bodies restrictors. This was clearly a little too coarse an adjustment so had to revert back and so instead dropped the WC curve down to 0.5 and now most of the TRV's don't intervene at all - the heating is on 24/7 with no setbacks in the main living areas and bedrooms - I still have a couple of areas where I am using scheduled heating (Front Hall, Study, Utility and Downstairs Loo) because these rooms either lose far more heat being on the north side of the house or have slightly oversize rads which makes them respond quickly to heat input.

 

Now all I need is a cold spell so I can see how the curve works with a much colder outside temp

 

Hope you all had a good Xmas and wishing you all a Happy New Year

 

[JohnMo]

19 minutes ago, marshian said:

WC is supposed to be better than that so I was a little disappointed.

All sounds good.

 

I found very similar at low flow temp WC (on warmer days) was really high consumption due to cycling. Actually found running slightly higher temps and bouncing of a thermostat was better, from a consumption perspective. Through experimenting found at 36 and below, boiler would cycle on off every 6 mins (or worse), but at 39-40 would run non stop for many hours if I wanted it too. First 20 mins would result in responsible consumption, but let it run way longer and the consumption drops really well. So nice long runs win for me, but I can charge my floor as a good buffer.

 

So you may be better finding the magic flow temp for very long running and use the thermostat to stop the boiler, so you don't overshoot room temp. I replaced my outside sensor with a fixed resistor, boiler thinks it 15 degs outside all year round. So runs in WC mode. Thermostat used to drop boiler in and out of set back mode

[marshian]

3 minutes ago, JohnMo said:

All sounds good.

 

I found very similar at low flow temp WC (on warmer days) was really high consumption due to cycling. Actually found running slightly higher temps and bouncing of a thermostat was better, from a consumption perspective. Through experimenting found at 36 and below, boiler would cycle on off every 6 mins (or worse), but at 39-40 would run non stop for many hours if I wanted it too. First 20 mins would result in responsible consumption, but let it run way longer and the consumption drops really well. So nice long runs win for me, but I can charge my floor as a good buffer.

 

So you may be better finding the magic flow temp for very long running and use the thermostat to stop the boiler, so you don't overshoot room temp. I replaced my outside sensor with a fixed resistor, boiler thinks it 15 degs outside all year round. So runs in WC mode. Thermostat used to drop boiler in and out of set back mode

 

I'm pretty sure that when I was in the middle stage I was getting a lot of cycling

 

Right now the number of cycles per day is between 14 and 21 (So less than 1 cycle per hour)

 

Watching the boiler yesterday it would burn for ~30 mins and be off for 45 mins - this was consistently the pattern throughout the day. (Fired 5 times overnight according to the ViCare app)

[JohnMo]

2 minutes ago, marshian said:

Watching the boiler yesterday it would burn for ~30 mins and be off for 45 mins - this was consistently the pattern throughout the day. (Fired 5 times overnight according to the ViCare app)

That sounds very well controlled.

 

You have your cold spell starting today if the weather forecast is correct. We have a 10 deg drop from midnight last night to midnight tonight 

[marshian]

13 minutes ago, JohnMo said:

That sounds very well controlled.

 

You have your cold spell starting today if the weather forecast is correct. We have a 10 deg drop from midnight last night to midnight tonight 

I’m fairly happy with it now - there are no low flow alarms - circuit is running constantly at 0.5 m3 per hour

 

Boiler on restart peaks at 50% modulation but rapidly drops to 10.6 % modulation and happily sits there for 30 mins before flow and return temp rise to the point the boiler turns off and waits for it’s restart point

 

Mean Rad temps are around 27 deg C and if flow temp is 30 deg return to the boiler is 24 deg C

 

Roughly 4.0 to 4.9 kWh per HDD so I am using a smidge more gas than scheduled heating (3.5 to 3.9 kWh per HDD) but the room comfort makes up for that - it wasn’t about saving energy it was about making a stable house temp

[marshian]

My octopus app says I used 8% more gas this last week 33.9 m3 than the previous week 31.4 m3

 

The local weather station HDD says last week was 74.9 HDD

The previous week was 64.9 so 15% colder

 

I'm going to chalk that up as a win

[marshian]

On 30/12/2024 at 10:57, JohnMo said:

I found very similar at low flow temp WC (on warmer days) was really high consumption due to cycling. Actually found running slightly higher temps and bouncing of a thermostat was better, from a consumption perspective. Through experimenting found at 36 and below, boiler would cycle on off every 6 mins (or worse), but at 39-40 would run non stop for many hours if I wanted it too. First 20 mins would result in responsible consumption, but let it run way longer and the consumption drops really well. So nice long runs win for me, but I can charge my floor as a good buffer.

 

So you may be better finding the magic flow temp for very long running and use the thermostat to stop the boiler, so you don't overshoot room temp. I replaced my outside sensor with a fixed resistor, boiler thinks it 15 degs outside all year round. So runs in WC mode. Thermostat used to drop boiler in and out of set back mode

 

How bloody right you are - today was 11.5 Deg C - flow temp target on the WC curve was 26 deg

 

Cycling wasn't great - rooms maintained temps but at the expense of frequent short burns over 30 burns so far today

 

I think the driver is the flow temp rises too fast for the boiler to modulate down rather than the circuit being too small

 

I increased the room temp target to 25 which skews the WC curve to be 34 at 10 deg C and got a couple of decent length burns at the expense of room temps bouncing of the TRV temp ceiling

 

I'm going to range rate the boiler to 5kW (or whatever % that works out to be) and see if that fixes the issue

[marshian]

With HW demand box it's not possible to cap the boiler output on HW mode (Viessmann Technical told me this when I asked how to stop the boiler throwing 19kW at a 3kW HW coil)

 

I know on CH it is possible and I know 10.6% is my boiler min (3.2 kW in low temp operation) because I've measure consumption at that rate in long stable burns.

 

I did a little study a while back on HW to see what the boiler was really kicking out

 

100% is 19 kW (on a 16kW rated boiler - go figure)

 

50% is 10 kW

 

33% is 7.4 kW

 

So I've set it to 20% and see if that stops the issue but still gives me some head room on restarts

[marshian]

On 31/12/2024 at 21:56, marshian said:

% Modulation declared in the ViCare app v actual boiler output

 

100% is 19 kW (on a 16kW rated boiler - go figure)

 

50% is 10 kW

 

33% is 7.4 kW

 

10.6% is 3.2 kW

 

So I've set it to 20% and see if that stops the issue but still gives me some head room on restarts

 

Quoting myself I've had to revisit the Range Rating setting as my initial impressions was that it wasn't actually working at all

 

Actually appears that it did but it's not what I expected............

I've got that menu sussed now - I write this stuff down because the boiler manual is pretty poor - see urban plumbers review of Viessmann Boilers and the sketch at the end - I'll link it below just for squits and giggles

So you would think with a range of settings from 9 to 100 it would be a % of output - It's clearly not!!!!

When I set it to 25 that is actually 15.7% of the output (after the initial fire up where it can go to around 60% and then stabilisation before modulating down to manage the flow and return temps)

Background to the discovery

I needed to increase the flow temps because water heating was 40 mins and the house temps had dropped a bit much to recover - Fridays is my legionella cycle and it's also Mrs BC's bath night so water in the morning is only heated to 45 for the showers - we have a fairly cold tank to re-heat to 60 to 65 deg C but that takes about 40 mins

So I raised the target room temp to 25 from normal 20 - this should have given me a flow temp of 39 deg (at 0 Deg outside) but it didn't it gave me 34

I backed the room temp down to 20 and raised the WC curve to 0.5 but plus 8.0 on the slope - this should have given me a flow temp of 39 deg (at 0 outside) but it didn't it stayed at 34.

The boiler modulation was 15.7% nailed there.

Ahhh lets look at the range rating I implemented

Menu b.2 Option 7 is setting max heating output

Quick experiment and I've got the table below
 

Setting	% Modulation	kWh
20	10.6	3.2
25	15.7	3.9
30	20.4	5.0
35	27.6	6.8
40	32.3	8.0
45	39.1	9.0
50	47.2	10.0

So the setting is not a % at all but just a number but now I've got a good guide for the % I might need when things warm up

Mean time I've left it at 40 because that gives me head room to accelerate house warm up if I need to and when it warms up again I can try a lower value (or faster pump speed)

Now last a link as promised (jump to 11 mins in for a summary of Szymon's experience during the install and watch to the end)

 

 

PS I still wanted a Viessmann boiler even after seeing that review because very few boilers come close to it's turn down ratio - I mean it can't be that hard to get it performing at it's best can it (Don't answer that..........)

Anyway house has responded to a burst of heat and I'm back to 0.5 and 1.0 level and I've learnt another element of control on the boiler

[Lofty718]

Interesting regarding range rating, my Vaillant is 30kw range rated down to 6kw and still cycles heavily, really annoying a year after I bought my boiler Vaillant then released the new ecotecs that modulate 1:10 rather than 1:5

 

You do know that cycling is not the end of the world though?  as long as you get a burn time of over 12 minutes or so each time then not much efficiency is being lost at all.

[marshian]

1 minute ago, Lofty718 said:

Interesting regarding range rating, my Vaillant is 30kw range rated down to 6kw and still cycles heavily, really annoying a year after I bought my boiler Vaillant then released the new ecotecs that modulate 1:10 rather than 1:5

 

You do know that cycling is not the end of the world though?  as long as you get a burn time of over 12 minutes or so each time then not much efficiency is being lost at all.

 

I can accept a level of cycling - less than 3 per hour would be my aim 

 

It's not just the efficiency loss from  excess cycling it's the wear and tear on the boiler components, expansion contraction, gas valve, igniter etc etc 

 

Old boiler peaked at 24 burns in an hour and I got a cooling house as an added bonus (don't over zone and don't try to achieve the biggest drop you can on each radiator flow and return were lessons learnt there)

 

New boiler set a record of 53 cycles in 8 hours per hour but that was down to 13 Wiser smart TRV's all having the ability to individually fire the boiler

 

They don't get to do that now

[marshian]

Warning - I may or may not be a little OCD on data collection and evaluation

 

Todays statistics

 

House Internal temps 18 - 20 deg

 

Outside temp C

Lowest -1.9

Highest 2.3

Average 0.2

 

Highest Boiler flow temp on CH 34.4

Highest Boiler return temp on CH 27.1

 

Currently 34.3 deg C flow temp

 

CH has been on for 14 hrs, HW for 30 mins so far today so total mins 870 mins

 

Total boiler burn time 600 mins

 

Number of starts 11

 

So boiler run time is 69% of the heating on time and average boiler burn time is 54 mins (Would be higher but it did 30 mins of HW and it always stops and restarts after doing the HW due to the 80 deg flow temp mandated by the HW Demand box)

[MrPotts]

6 hours ago, Lofty718 said:

Interesting regarding range rating, my Vaillant is 30kw range rated down to 6kw and still cycles heavily, really annoying a year after I bought my boiler Vaillant then released the new ecotecs that modulate 1:10 rather than 1:5

 

You do know that cycling is not the end of the world though?  as long as you get a burn time of over 12 minutes or so each time then not much efficiency is being lost at all.

At the moment my gas boiler is igniting 6 times an hour controlled by my Wiser controls so maximum burn time is 10 minutes. I have tried to adjust the ignition to 3 times an hour but the setting doesn't work despite the Wiser hub confirming it is set correctly in the configuration. I have an open support ticket with wiser on this.

[marshian]

29 minutes ago, MrPotts said:

At the moment my gas boiler is igniting 6 times an hour controlled by my Wiser controls so maximum burn time is 10 minutes. I have tried to adjust the ignition to 3 times an hour but the setting doesn't work despite the Wiser hub confirming it is set correctly in the configuration. I have an open support ticket with wiser on this.

 

I had mine set to an "oil boiler" before I went 24/7 that tempered the Wiser unit from intervening as often

[John Carroll]

7 hours ago, Lofty718 said:

Interesting regarding range rating, my Vaillant is 30kw range rated down to 6kw and still cycles heavily, really annoying a year after I bought my boiler Vaillant then released the new ecotecs that modulate 1:10 rather than 1:5

 

You do know that cycling is not the end of the world though?  as long as you get a burn time of over 12 minutes or so each time then not much efficiency is being lost at all.

 

If you can believe the below, then any run time of more than 3 minutes per cycle has a negligible effect on boiler efficiency.

[Sparrowhawk]

7 hours ago, marshian said:

Number of starts 11

Is there somewhere in the ViCare app to see the daily starts? I can only find the total under Diagnostic Information

[marshian]

35 minutes ago, Sparrowhawk said:

Is there somewhere in the ViCare app to see the daily starts? I can only find the total under Diagnostic Information

 

Absolutely correct but it's not hard to log the totals by day and as a result get the daily number of starts

 

Or perhaps that's just me being typically OCD

[marshian]

56 minutes ago, John Carroll said:

 

If you can believe the below, then any run time of more than 3 minutes per cycle has a negligible effect on boiler efficiency.

 

I've seen that before and I reckon it's flawed because it doesn't take into account the increase in modulation on start up - my old glow worm boiler took 4 mins to drop down to 10 kW from it's fire up at 85% of max (which is actually fairly typical of many boilers)

[JohnMo]

I am currently controlling my boiler burns, by finding the temperature it likes to run without stopping. Which is 39 degs. Found it was happy to run for hrs - charging a thick screed floor. Boiler min turn down is supposed to be around 6-7kW against a current heat demand of less than 3kW.

 

Have had to fool the boiler in to thinking it's running WC, with a resistor. Found anything below about 36 Deg flow temp cycling was pretty bad.

 

I then run a set of simple home assistant automations, which tells the boiler to fire up at a given return based on outside temp. I then tell boiler to run for between 1.5 to 2 hours. Bit like WC but less stop start cycling and on a fixed flow temp. I am also able to adjust the gradient of the startup so it adds 3 degs max to start up temp, so takes 11 to 12 mins to get up 39 degs generally.

 

So far today (currently -5, and high of about +2 today) boiler has started 5x for heating and 2x for DHW.

 

Have found the gas consumption pretty low and compared to cycling very low.

[marshian]

6 hours ago, JohnMo said:

I am currently controlling my boiler burns, by finding the temperature it likes to run without stopping. Which is 39 degs. Found it was happy to run for hrs - charging a thick screed floor. Boiler min turn down is supposed to be around 6-7kW against a current heat demand of less than 3kW.

 

Have had to fool the boiler in to thinking it's running WC, with a resistor. Found anything below about 36 Deg flow temp cycling was pretty bad.

 

I then run a set of simple home assistant automations, which tells the boiler to fire up at a given return based on outside temp. I then tell boiler to run for between 1.5 to 2 hours. Bit like WC but less stop start cycling and on a fixed flow temp. I am also able to adjust the gradient of the startup so it adds 3 degs max to start up temp, so takes 11 to 12 mins to get up 39 degs generally.

 

So far today (currently -5, and high of about +2 today) boiler has started 5x for heating and 2x for DHW.

 

Have found the gas consumption pretty low and compared to cycling very low.

That is an excellent result but maybe way outside the abilities of most people 

 

All I’m trying to do with this boiler is get it running at it’s optimum when matched to the house needs using the parameters that i have control over - I think I’m fairly close to where it’s doing decent length cycles at low flow temps and maintaining the house at a comfortable temp without burning excessive amounts of gas.