Viessmann Vitodens 200-w - initial impressions

[Nickfromwales]

Systems get regularly and repeatedly topped up, for sealed and pressurised systems, so there will be a life-long influx of fresh oxygen rich water which is the reason that the inhibitors presence is of importance. 
 

[markocosic]

Strongly disagree. 

 

 

Nice old iron systems have corrosion allowances. You fill them; you let them corrode; this consumes the oxygen in the water. The boilers god first. They corrode from the inside and they corrode from the outside (all the acidic nasties in the dirty wood / coal / oil that you're burning that eat the heat exchanger even if you try to prevent condensing operation by keeping return temperatures high enough). Pipework doesn't tend go because systems are arranged so that all the muck and air end up in the radiators. 100 years isn't a problem. A pH between 8.2-10 is fine and that's what you water ends up at naturally due to corrosion by-products.

 

 

More recent open-vented systems with copper pipework, thin steel panel radiators, and noncondensing iron boilers are ok provided that they're not leaking and the header tank is being used for expansion not for constant fill. The rads and boilers last 30-50 years; at which point the rads are scruffy and the valves have all stuck or started to weep and the boiler is at the end of its service life etc. You replace the lot and you're fine. No inhibitors. Muck about replacing them piece by piece and yes, I agree, you'll keep on introducing oxygen that soon turns to rust and sludge. It's that sludge that'll kill you (bunging up the pump and valves and boiler) before the corrosion allowance on the radiators or boiler is a problem. Bunging in some inhibitor instead of replacing the pumps, rad valves, and boiler at the same time and leaving it filled for another decade isn't smart though; and if you do maintain it properly then you don't get that regular topup that introduces oxygen. 

 

A pH between 8.2-10 is fine and that's what you water ends up at naturally due to corrosion by-products. If you stick inhibitors in you 

 

 

New closed systems with stainless boilers and panel radiators or oxygen-barrier-ed underfloor are fine. You fit 'em. You flush 'em. You fill them. You bleed them and top them up once the corrosion has happened. You leave them alone for a decade. You drain them. You replace the expansion vessel. You fill them. You bleed them. You leave them alone for another decade. No inhibitors. They're not necessary in these systems that don't leak and don't break and don't require regular topups. If they do leak all the time and break down all the time you've got other issues. (low quality install; low quality equipment) Again a pH between 8.2-10 is fine and that's what you water ends up at naturally due to corrosion by-products.

 

 

The nightmare scenarios are:

 

1) rubbish old system that gets converted from open vented to closed and runs at 2.5 bar not 0.5 bar; with valves whose seals weep and joints that aren't tight; so it it leaks like a sieve; plus an el cheapo boiler with aluminium heat exchanger; and an energy efficient circulator pump that contains permanent magnets to ensure that all the sludge builds up inside it. Now you've got a constant oxygen supply to turn into sludge and you simultaneously need to keep the pH low (for the aluminium - between 6.5 and 8.5) whilst also keeping the pH high (for the steel - between 8.2 and 10). You can do it, using buffers to control pH and inhibitors to control corrosion. It's a finicky (impossible) thing to maintain though. 

 

2) new system installed by monkeys; preferably underfloor heating without an oxygen barrier (to ensure that oxygen keeps coming in even though you're not toping up the water); paired with an aluminium boiler (difficult to protect); filled from a high conductivity salt-softened supply (conductivity speed corrosion); kept under-pressurised (so that you get lower pressure around valves etc that sucks in oxygen through the seals); and installed with an energy efficient circulator pump as above.

 

 

If the system is godawful then inhibit it. If the system is tight then fill it, forget about is for a decade or more, then do the occasional major service including *preventative* maintenance (replacing the bits that you know will fail) every 10 years or whenever a major component fails.

 

Expansion vessels should be oversized and installed external to the boiler (give them an easy life) Isolation valves should be exercised annually. (so that your pump or even your boiler CAN be swapped without a full system drain) Valves shouldn't be toolfix own brand specials. And don't buy boilers with aluminium heat exchangers  - unless the system is entirely underfloor heating and/or aluminium radiators. You're planning for failure by doing this.

 

I'd avoid thinwall carbon steel pipework unless employing a water treatment professional too. It can work. It can also go very badly wrong very quickly. (you MUST flush it then immediately fill it and keep it filled - allowing it to dry will initiate localised corrosion and pinhole it in no time)

 

 

(day job is district heating systems for what it's worth; so get to see lots of examples of water treatment done right on state-of-the-ark systems along with water treatment gone wrong on modern systems)

 

Build the system from compatible materials. Keep it tight. Don't keep taking it to bits. Everything but the heat source and circulator pump/expansion vessel is capable of lasting longer than you'll be alive. Without inhibitors. There's a standard for it called VDI2035. If you don't follow that standard your boiler warranty - if a premium brand from the continent - will probably be void. There's a reason for it.

Those trade mags and the 17 year olds in the blue vans sponsored by british gas and worcester-bosch and fernox are paid to spout everything that you need to know to make sure the system won't last 15 years. ? 

[markocosic]

When it comes to tightness testing you'll need something like this:

 

https://www.ebay.co.uk/itm/363143285529

https://www.ebay.co.uk/itm/254953023280

 

I'd expect to see a radiator system - except for the expansion vessel and the boiler / pressure relief valve - tested to 10 bar cold.

 

I'd expect to see potable water systems - except for any cylinder / expansion vessel / pressure relief valve - tested to a minimum of 10 bar cold; preferably 20 bar where the components (pipe, taps etc) allow this. Most will.

 

Bring it up to pressure. Wait 10 mins for everything to stretch/settle. Bring it up to pressure again. Wait 20 minutes. Bring it up to pressure again. Wait 2 hours. Check how much it's moved vs what the pipework vendor allows. (the initial stretch in PEX is a LOT; in copper it's not a lot / anything more than 0.5 bar is a massive red flag)

 

You rarely see this in domestic installs but you should. It quickly finds all your iffy / forgotten joints.

 

You see it more often in district heating land (many old systems are drained every spring and pressure tested over the summer - cold - after all the annual maintenance before they're allowed to be filled hot) and in newbuilds (the primary pipework on 50+ storey towers is at thoroughly decent pressure; and your insurers will want to make darn sure that the penthouse isn't about spill it's guts onto the deputy penthouse below)

[larry]

Okay quite a lot of this is going over my head but I said I'd update on the 200-w and how this has gone. 

Same problem back again. 

Boiler heating on minimum burner when no heating demand. Seemed more intermittent than previous but just as annoying. Have to turn the DHW off and on before using the shower...

So we'll ask veissman to take a look again...

And I'll update again on here. 

 

[larry]

On 12/05/2021 at 22:30, larry said:

Okay quite a lot of this is going over my head but I said I'd update on the 200-w and how this has gone. 

Same problem back again. 

Boiler heating on minimum burner when no heating demand. Seemed more intermittent than previous but just as annoying. Have to turn the DHW off and on before using the shower...

So we'll ask veissman to take a look again...

And I'll update again on here. 

 

Latest update: Veissmann engineer has attended and diagnosed a faulty diverter valve. New valve being ordered and being replaced next week. Impressed with Veissman's quick follow-up on this and keeping fingers and toes crossed the engineer is right. 

[PeterW]

2 minutes ago, larry said:

Latest update: Veissmann engineer has attended and diagnosed a faulty diverter valve. New valve being ordered and being replaced next week. Impressed with Veissman's quick follow-up on this and keeping fingers and toes crossed the engineer is right. 

Given that is the core component in a combo boiler and it’s less than 6 months old, it kind of puts it firmly on the “do not specify” list. 

[larry]

On 14/05/2021 at 10:58, PeterW said:

Given that is the core component in a combo boiler and it’s less than 6 months old, it kind of puts it firmly on the “do not specify” list. 

 

Next update. Viessmann engineer has visited again and replaced faulty diverter valve. It made no difference, so that's not it!

Lots of head scratching. 

He's now going to replace the 'hydraulic block' (I may be using the wrong words, it was definitely a 'block' of sorts!) which apparently he has never had to do before. 

In the meantime, I have fiddled with the settings a little and found that I partly solved it through increasing the 'minimum burner output' setting, up to about 15% from 5% previously. However, the boiler still seems to be dumping hot water to the radiators whilst there is a call for DHW and no call for heat. And, of course, my main reason for buying the boiler was because of the ability to modulate output magnificently, which of course this then obviates somewhat. 

Engineer visiting again this week. We'll see what happens. And I'll update on here. 

[larry]

10 hours ago, larry said:

 

Next update. Viessmann engineer has visited again and replaced faulty diverter valve. It made no difference, so that's not it!

Lots of head scratching. 

He's now going to replace the 'hydraulic block' ....

Engineer visiting again this week. We'll see what happens. And I'll update on here. 

 

OK, so I promised an update. Viessmann engineer has visited today again. 

He has replaced the hydraulic block.

He has also replaced both control boards on the boiler. 

Probably spent about 4 hours with the thing. The poor chap.

Seemed to be working when he left but.... no dice. 

As soon as I turn the 'minimum burner' setting to 10% then the burner will not switch off when there is a call for DHW. 

With the setting above 10%, then the burner will turn off and it appears to operate properly. However, in all cases, whilst there is a call for DHW the boiler is dumping hot water to the heating circuit (not just afterwards, but whilst the tap is running).

So, basically he's fitted us pretty much almost a whole new boiler and we still have the same problem. So, my logic is it can only be a 'settings' issue or a 'system' issue. 

The fact that the boiler worked fine for 8 weeks or so and the problem appeared out of the blue seems a bit mysterious.

The fact that our previous installation worked fine with our old Baxi combi boiler and this just just been fitted to the same pipework seems to point against a system issue?

Interestingly, the Viessmann engineer tells me that when the heating circuit is fully closed off the boiler seems to behave itself. 

So... not quite sure where to go next, other than back to the installation company again.

Might try isolating the rads one at a time to see if that makes a difference.... though I really can't be bothered! 

I will post in here and updates and any smart ideas are welcomed. 

 

So... going back to the original question: would I buy the boiler again now? No. Not really. 

  

 

[markocosic]

To try identify your issue:

 

Boiler fires when flow sensor detects dhw flow.

 

Boiler should divert flow through dhw plate heat exchanger not through space heating circuit when there is dhw flow 

 

Boiler should modulate burner output to match the dhw flowrate 

 

The boiler will fire whilst there is dhw flow. It will keep firing until the plate heat exchanger is up to temperature. (so that you can restart a paused shower without getting a slug of cool water)

 

There is flow into the space heating circuit when there is dhw flow though.

 

This flow is big enough that anything less than 10% burner results in so much heat thing into the space heating circuit that the plate heat exchanger never reached the set point.

 

Why is there flow?

 

- diverter valve fault

- diverter actuator fault

- controls fault driving diverter open

 

- external driving forces that shouldn't be there (e.g. external circulation pumps)

 

A service tech should be able to identify the first three. You check the first one by closing the valve by hand and seeing if you get this back flow. You check the second by removing the actuator and verifying how it moves. The third is identified if the first two pass.

 

The latest is possible. System diagram?

 

If the latter I'd guess your previous boiler either didn't have the "keep plate warm after hot water is used" feature or had a different diverter valve arrangement that wasn't as sensitive to external driving forces.

 

 

 

 

[markocosic]

Hang on a sec...re-reading the initial thread....you have set this to 'continuous heating' mode and are surprised that it is....heating continuously?

 

In that mode it will keep the heating pipework up to temperature...continuously.

 

So unless your controls are setup for this (with valves that close off each zone when the desired temperatures are reached) is the boiler not doing exactly what you've asked it to do? (keep space heat hot 24/7/365) 

 

And you're noticing a "fault" because your heating system is "calling for heat" (by virtue of having open valves even though rooms are at temperature) even though your rooms are up to temperature?

 

i.e. The consumer side controls aren't designed appropriately for a 'continuous heat' source.

[larry]

On 03/06/2021 at 09:40, markocosic said:

Hang on a sec...re-reading the initial thread....you have set this to 'continuous heating' mode and are surprised that it is....heating continuously?

 

In that mode it will keep the heating pipework up to temperature...continuously.

 

So unless your controls are setup for this (with valves that close off each zone when the desired temperatures are reached) is the boiler not doing exactly what you've asked it to do? (keep space heat hot 24/7/365) 

 

And you're noticing a "fault" because your heating system is "calling for heat" (by virtue of having open valves even though rooms are at temperature) even though your rooms are up to temperature?

 

i.e. The consumer side controls aren't designed appropriately for a 'continuous heat' source.

Hi Mark, thank you so much for these replies. Your first post particularly I think really helps me get my head around what the boiler likely thinks is happening here in regards to trying to keep the plate exchanger up to temperature but failing. I do think the engineer who has visited as tried to rule out the first three options, certainly new diverter valve, and replaced logic boards. He's also I think said he's tested the switch etc. 

 

In regards to the 'continuous operation' mode, this was exactly what was advised by Veissmann. I was completely surprised also. I think it is essentially 'not weather comp' mode. The service engineer who has visited has recommissioned the boiler (several times) and kept it in this mode. It has a 'switch off in reduced mode' function, which turns the pump off when there is no call for heat, and seems to essentially be to keep the flow temp to 20'c when there is no call for heat/DHW. 

 

In terms of a diagram, it's a pretty simple setup. Two main 22mm pipes with 15mm branches. The 22mm pipes drop downstairs to feed most of the rads downstairs except one, which is on a separate 15mm drop (concrete floor). No pumps. About 16 rads in total, reasonably large detached house. Engineer opined there might be a 'short circuit' somewhere in the pipework or some kind of crossover - Whilst I suspect some of the rads are the 'wrong way around' I don't think there's more than this as I've seen the majority of the CH pipework under floors/above ceilings etc but my next plan is to turn all rads off from the lockshields and see what happens. If that fixes it, then to open the rads one by one. 

 

Ultimately, it's a 3 month old installation with a '15 year guarantee' so this really should just be for Veissmann and the installatio company to sort out, but I want to be a helpful customer!!

 

[larry]

This is hopefully (!) the final update on this thread... we have had a couple more callouts and the engineer has replaced the 'bypass cartridge'. He sounded very confident that this would be it so I have fingers and toes crossed that he's right. I'll update again if the problem re-occurs  

[Nickfromwales]

?. Bypass normally only allows the pump to recirculate back to itself via the return, so the pump needs to be going before the bypass could ever be an issue.

The pump should not be running if there’s no call for heat, so I am dubious about that being a solution tbh. 
Stunk of diverted valve issues, but you say that’s been replaced? 
Most combi boilets go into pump overrun after DHW has been drawn, to get rid of the nuisance heat, the high temp heat left in the primary heat exchanger, and that goes to the heating circuit but without a flame. Eg the boiler sucks cool or cold water from the central heating into the HEx to cool itself down for between 1 and 2 mins typically. Then the pump should shut off.

 

Ok;

PS. Wow!  You are the most patient person I’ve ever heard of. By now it would have been off the wall and dropped off at the point of purchase with “return to sender” written on it in permanent marker.

 

[markocosic]

It's working exactly as intended and the manual suggests.

 

The control strategy for space heating being used is not appropriate.

 

This UK Viessmann rep seems to be a tool. Nice but dim or smarter than he looks and paid by the callout?

 

In order to use the boiler in the mode selected the storage heating needs to be fully zoned. If a zone is open (if there is flow when they pump starts up) then the boiler will run until the heating circuit achieves the set temperature.

 

This works great in a system that has radiators and TRVs everywhere with no bypasses. It will run until the pipework within the bigger achieves setpoint then it will stop.

 

It works where there is a towel rail too. That'll always be kept warm even if all your TRVs are closed.

 

Your system design is wrong for this operating mode. If somebody did you a system then ask them to fix it. (using zone valves) If the vendor sold you a m is s-boiler for that system then they'll need to fix the system (using zone valves) or cut their losses and remove the boiler for a refund.

 

If you keep letting numpty or callout collector take the boiler to bits it's going to be a wreck. Every time seals are broken and wires pulled out you're inviting another opportunity for things to be damaged and fail later IMO.

 

 

[larry]

OK - well it's only been a day, but I'm also saying this seems to be fixed. I can turn the hot tap on and the heating pipes no longer start getting hot immediately. And, even on minimum burner output, the boiler fires up, makes the water hot, and then turns off again. 

 

Mark I have to say I'm not 100% sure I completely understand what you're saying, but if the rads now get hot when they should do and the DHW now gets hot when it should do, and it doesn't seem to be doing anything it shouldn't be doing, what's the problem? It's working just like our previous combi boiler was working?

 

Nick, I suspect my patience might have been thinner if this was January    I have to say I was generally impressed with Veissmann. OK, so it took just a little while for them to figure out the problem (!) but there was no issue in getting them to come out whenever I called up and the engineer did seem to invest a lot of effort to sort things out.

 

[markocosic]

How's the weather?

 

Hot enough that the space heating puppies are already at the weather compensated setpoint?

 

I'd wait for cooler weather to decide that this is fixed.

[larry]

1 hour ago, markocosic said:

How's the weather?

 

Hot enough that the space heating puppies are already at the weather compensated setpoint?

 

I'd wait for cooler weather to decide that this is fixed.

Haha, fair point Though we've got weather comp off and when I put the Drayton Wiser system onto 'boost' the heating kicks in as I'd expect.

But yes, fair enough - I'll update in November!!

[markocosic]

So you've turned off "continuous operation" mode... switching to a non weather compensated "in response to a call for heat" mode...and surprise surprise it's no longer operating continuously?

 

That's the fix. Setting the boiler to not try and keep the side heading circuit hot 24/7/365; and to instead respond to a (non opentherm) call for heat.

 

Not all the random swapping of parts by vaillant.

 

Switch the mode back and you'll restore the previous behaviour.

 

 

 

[larry]

14 hours ago, markocosic said:

So you've turned off "continuous operation" mode... switching to a non weather compensated "in response to a call for heat" mode...and surprise surprise it's no longer operating continuously?

 

That's the fix. Setting the boiler to not try and keep the side heading circuit hot 24/7/365; and to instead respond to a (non opentherm) call for heat.

 

Not all the random swapping of parts by vaillant.

 

Switch the mode back and you'll restore the previous behaviour.

 

 

 

I'm as perplexed as you are Mark, but the boiler remains in continuous operation mode. The setting "switch off in reduced mode" is turned on (and has been since install). Viessmann (not valliant) advised that this was the right mode for our setup, this from the central technical team as well as both technicians who visited and the installer. I realise it doesn't make sense but it seems that continuous operation mode on this boiler does not mean what it says on the tin, at least if the "switch off in reduced mode" setting is on. The problem was present prior to the most recent visit by viessmann, they have changed the bypass cartridge and the problem no longer appears to be present. If that's helpful for anybody struggling with a viessmann 200 where it looks like a diverter valve problem but isn't, I'd be delighted. 

I promise I'll update if things change either with the fault recurring or when we get to weather that needs regular heating! 

[larry]

On 14/07/2021 at 15:05, Nickfromwales said:

?. Bypass normally only allows the pump to recirculate back to itself via the return, so the pump needs to be going before the bypass could ever be an issue.

The pump should not be running if there’s no call for heat, so I am dubious about that being a solution tbh. 
Stunk of diverted valve issues, but you say that’s been replaced? 
Most combi boilets go into pump overrun after DHW has been drawn, to get rid of the nuisance heat, the high temp heat left in the primary heat exchanger, and that goes to the heating circuit but without a flame. Eg the boiler sucks cool or cold water from the central heating into the HEx to cool itself down for between 1 and 2 mins typically. Then the pump should shut off.

 

Ok;

PS. Wow!  You are the most patient person I’ve ever heard of. By now it would have been off the wall and dropped off at the point of purchase with “return to sender” written on it in permanent marker.

 

Ps, yes nick, bypass valve was replaced (twice!). And it wasn't just dumping heat to the rads after a call for DHW but from the very moment a call for DHW started. 

[Nickfromwales]

2 hours ago, larry said:

Ps, yes nick, bypass valve was replaced (twice!). And it wasn't just dumping heat to the rads after a call for DHW but from the very moment a call for DHW started. 

That means the diverter valve is not parking in the fully closed position. Most diverters park in the heating position, and then move to DHW position swapping duties 100%. 
The diverters park in the heating position to do pump overrun, the heat dump cycle after each burner ignition event. Yours is not getting 100% of the way closed aka diverted, therefore you have the heat leak to the rads.

I have to be honest, you need to remove this and get a full refund. Go grab yourself a Vaillant and get on with your life. Intergas and Veissmann do some strange choppy-changy is it a system boiler or is it now a combi nonsense and I’m not a fan at all.

You’ve done the polite customer to the extreme, now you just need to contact them in their UK offices and ask for the unit to be removed and draw a line under it. Can you imagine sorting this and then going to the same bunch of clueless halfwits for the next problem ?!? Time to call it a day I think, before winter when you really need it to work reliably.

Edited July 17, 2021 by Nickfromwales

[Nickfromwales]

I had exactly the same issue(s) with a Worcester Bosch boiler serviced via a British Gas ‘insurance plan’. BG came out, 5 engineers over 4 visits, fault not cured, and basically rebuilt the boiler in situ from bottom to top. Left the box of spares in the utility room as a trophy, to demonstrate how they’d done “everything possible” and they then left with the client having no heating or DHW. Told him he needed a new boiler and said they’d post a quote.

I went there, and 45 mins later I had the boiler working perfectly. Client was sooooo pissed off he rang the area manager ( the 5th chap you accompanied the final service engineer ) and gave the phone to me. The guy asked me what I did to fix it and I told him to keep guessing. So fed up of visiting customers ( pensioners mainly ) who have been a victim of this tactic from BG. I had to threaten them as a company to come and rectify a list of faults, one which was lethal, and gave them an hour to respond before I called the GSR to report them. After a load of condescending threatening waffle, 40 mins or so later 2 BG vans materialised. They told these pensioners that they needed new controls and the £5k glow worm boiler ( £600 in my plumbers merchant btw ) they just fitted ( in a day ) had to be left off indefinitely.
I was contacted by the electrical firm that BG eventually appointed to try and fix it, 3 days after leaving an immediately unsafe installation and an 82 & 83 year old without heating or hot water, and I couldn’t believe how bad a job they’d done. All they had to do was wire a modern system boiler to a standard S plan system. Ffs. 

All these “heating engineers” these days are just plug n play laptop jockeys who cannot think outside the box. Get them back into proper apprenticeships!!!!

[Adsibob]

@larry did you install the external temperature sensor, which I assume is for weather compensation? Manual says: to install on a "North or north-western wall, 2 to 2.5 m above ground level; in multi storey buildings, in the upper half of the second floor ■ Not above windows, doors or vents". This is a problem for me as my building, being a semi detached, has it's northern wall attached to my neighbour! Although actually we have just extended, so the northern side of my extension is exposed, but neighbour could easily build over it.

[larry]

On 23/11/2021 at 18:50, Adsibob said:

@larry did you install the external temperature sensor, which I assume is for weather compensation? Manual says: to install on a "North or north-western wall, 2 to 2.5 m above ground level; in multi storey buildings, in the upper half of the second floor ■ Not above windows, doors or vents". This is a problem for me as my building, being a semi detached, has it's northern wall attached to my neighbour! Although actually we have just extended, so the northern side of my extension is exposed, but neighbour could easily build over it.

 

Hi sorry for a v slow reply - but no, we did not install a temperature sensor. Our boiler operation is therefore not weather compensated. In any case, I don't think we could utilise a temperature sensor for weather comp since our operation is controlled by the Drayton Wiser system (which just turns on/off)

[larry]

I'm pleased to update we've got through the first chunk of the first full winter with no problems whatsoever after the 'bypass cartridge' was replaced. We've had our first service also (boiler engineer completely perplexed he was coming out to such a new  boiler but I want to maintain the 10 year warranty!). Working really well. And gas usage does seem somewhat down on our old baxi, though there are other factors also that will have contributed to that. V happy with the boiler set up now. Love the Viessmann app and the Drayton Wiser system that's controlling it is brilliant.