Viessmann Vitodens 100-w maintaining temp problem

[Dr911t]

I have a 2017 Viessmann Vitodens 100-W condensing gas boiler connected to a radiant floor heating manifold. No external pump. 120m2 floor area. Recently had the annual service. Boiler has been on for about a week now heating the underfloor heating cement slab.

It is my impression that the boiler seems to have trouble maintaining the central heating temperature (at any rotary dial setting) on the digital display.

Burner starts and heats up water (central heating side), only 1 bar on the modulation indicator, heats to ~40-50C for 30 seconds then stops and water temp goes down always to 24-27C for some minutes then the short cycle starts again ... Same symptom all dial settings 1-2-3-4-5.
Outgoing water pipe is hot initially but does not stay hot. The return of the central floor heating water is colder to the touch ~25-26C. Floor temp is around 22-24C. Temperature in the rooms 20.5-22C. Room thermostat on MAX in order to keep the flow open (could this be an issue? - I wanted to see how hot the rooms would get). Rooms further away from the boiler seem colder by ~2C. Didn't notice this last year.

Outdoor temp here now is around +14C day +2C night.
No outdoor sensor installed. No error codes.
Previous years have had central heating dial set between 3-4 and that gave a constant flow temp of around 35-45C as I remember. Do not recall this odd start/stop pattern. Previous heating seasons rooms at 23-24C and floor ~25-27C.
Domestic hot water is functioning fine. Set between 4-5. Slightly slow to heat up but gets to 60-70C and holds there temp for showers.

Any thoughts or am I just being worried for nothing?

 

[Dr911t]

Some videos of the short cycle and 'odd noise':
https://sendvid.com/3wa0f0eq
https://sendvid.com/x7z1px7i

 

[Dr911t]

Update on the problem - here is what the Viessmann tech did so far:
* Replaced plate heat exchanger
* Flushed floor heating & added ADEY MC3+ to the floor heating system
* Replaced boiler internal circulation Grundfos pump
* Power flushed with chemicals/acid the main heat exchanger

Next step diagnosis from Viessmann tech: clogged heat exchanger - replace it.

 

[BlueLoo]

Jeysus, a new boiler would have been cheaper....

Ask him why all that stuff needed changing. Ask him what is causing the blockages that need the arse of the boiler being ripped out and what he recommends to stop it happening again.

That's a lot of work for it to happen again in the future.

 

[Dr911t]

Jeysus, a new boiler would have been cheaper....

Ask him why all that stuff needed changing. Ask him what is causing the blockages that need the arse of the boiler being ripped out and what he recommends to stop it happening again.

That's a lot of work for it to happen again in the future.

Well it was a step-by-step replacement.. maybe it's this, maybe it's that. Two Viessmann authorized techs. Viessmann said probably blocked heat exchanger causing the blockage.
Due to calcifying and improper heating water used. Apparently the installer filled it with tap mains without adding any inhibitor and it's been running like that for 4 heating seasons.

 

[BlueLoo]

Well it was a step-by-step replacement.. maybe it's this, maybe it's that. Two Viessmann authorized techs. Viessmann said probably blocked heat exchanger causing the blockage.
Due to calcifying and improper heating water used. Apparently the installer filled it with tap mains without adding any inhibitor and it's been running like that for 4 heating seasons.

Replace bits until it starts working again huh. Some "techs" they are.
But then again, that's easier and quicker for the techs, rather than cheaper for you.
Calcifying? Like, does this have a constant fresh water flow through it? If it isn't the combi version, then the answer is no and you'd only have so much harness in the water from the start.
How do they know there is no inhibitor in it? Did they do a water test?
Why would you replace the pump for this? its not that old, just open it up, check and clean. I doubt the bearings or impellers are in a bad state (could be, dunno).
Where is the corrosion coming from that has knackered the system so bad? Its UFH which is plastic piping? There is no metal to corrode except for the boiler internals.

Seems to me to be a load of ******. They are just swatting at the thing to get it working.
Is this under guarantee? Would explain the part-bin mania they have.

 

[Dr911t]

Replace bits until it starts working again huh. Some "techs" they are.
But then again, that's easier and quicker for the techs, rather than cheaper for you.
Calcifying? Like, does this have a constant fresh water flow through it? If it isn't the combi version, then the answer is no and you'd only have so much harness in the water from the start.
How do they know there is no inhibitor in it? Did they do a water test?
Why would you replace the pump for this? its not that old, just open it up, check and clean. I doubt the bearings or impellers are in a bad state (could be, dunno).
Where is the corrosion coming from that has knackered the system so bad? Its UFH which is plastic piping? There is no metal to corrode except for the boiler internals.

Seems to me to be a load of ******. They are just swatting at the thing to get it working.
Is this under guarantee? Would explain the part-bin mania they have.

It's a combi condensating boiler. Connected to DHW and to UFH which is just plastic yes. No rads. Only new copper piping from the boiler to the mainfold. No external pump. There is fresh water for DHW but that goes through the plate heat exchanger, not the main one. They are saying the main one is clogged where the central heating water is circulating.

Commissioned 5y ago and filled with mains water. Treatment unknown as boiler installer retired and is unreachable. No water test. But was partially flushed previous services and water was quite dirty looking. Some black metal pieces like oxide floating around.

I hear you mate, maybe you wanna pop over the pond and take a look
I'm just so frustrated with Viessmann -- all they do is say to call up their authorized service partners. We called 30 and managed to get 2 to eventually come out. Viessmann will not take back any installed parts even if installed by their authorized service partners. Just out of warranty too.

 

[Gasguru]

In order to become an authorised installer most manufacturers require you to attend a days course in their product range ie. how to flog their boilers.
It has little to do with technical competence...some of the worst installs I've seen have been by Worcester approved installers eg. flow & returns reversed, installed in compartments where the casing can't be removed.
Your first mistake was to get a Viessmann...they are extremely niche market and most sensible installers give them a wide berth due to the extortionate parts prices/availability and over complex manuals/design.

Run the boiler at 1 bar max with the system cold...2 bar is way too high.
What does the benchmark commission sheet say (although many are falsified)...normally at the back on the manual although Viessmann may be different.
Why are you paying for parts if the fault has not been correctly diagnosed?
If the hot water is working ok then that normally proves most of the boiler is ok, even minor blockages in the primary heat exhanger/plate heat exchanger or a weak pump can show up as a reduced hot water performance.
When you say no external pump fitted do you really mean there is no pump on the underfloor manifold?
Post a pic of the manifold.

 

[Dr911t]

In order to become an authorised installer most manufacturers require you to attend a days course in their product range ie. how to flog their boilers.
It has little to do with technical competence...some of the worst installs I've seen have been by Worcester approved installers eg. flow & returns reversed, installed in compartments where the casing can't be removed.
Your first mistake was to get a Viessmann...they are extremely niche market and most sensible installers give them a wide berth due to the extortionate parts prices/availability and over complex manuals/design.

Run the boiler at 1 bar max with the system cold...2 bar is way too high.
What does the benchmark commission sheet say (although many are falsified)...normally at the back on the manual although Viessmann may be different.
Why are you paying for parts if the fault has not been correctly diagnosed?
If the hot water is working ok then that normally proves most of the boiler is ok, even minor blockages in the primary heat exhanger/plate heat exchanger or a weak pump can show up as a reduced hot water performance.
When you say no external pump fitted do you really mean there is no pump on the underfloor manifold?
Post a pic of the manifold.

New to gas boilers, lived in warmer climate before. It's what the builder suggested, did some research and they were quoted as high quality, long lasting boilers.
It's running at 1.5 bar warm now, doesn't reach 2 after the latest flush. Guess the previous techs left it too high, nice.
Paying for parts: all these guys do is order from Viessmann. Local Viessmann headquarters in my country confirmed they don't take parts back once installed. Local policy or Viessmann everywhere is like this? I don't know. So they the 'techs' try a part, doesn't work and leave it in. I'm 1000 in the hole now and i'm ready to throw it out the window before spending more on the main heat exchanger. These were two diff techs from two different authorized service partners.

hot water is not 100% ok, it's running 'hot'.. 75-80c and sometimes cuts out. pump new, plate exchanger new.

i'll try to get a manifold pic later but we are on a single floor 120m2 with 9 loops, 6 thermostats and it's been working 'fine' for 5y with good flow. the circulation pump in the combi boiler was moving the water around just like it would be moving it around rads but we have no rads. that's how the installer did it, didn't have much input as it's not my area of expertise and I thought I had 'the experts' doing it.

 

[Gasguru]

Only ever use a builder for building work. Always use individual trades for plumbing/heating/electrics etc. Builders will maximise their own income if you let them bring in the other trades and always problematic.
Parts availability, sensible parts prices, good manufacturer backup, widespread knowledge of the model etc trumps any magazine/installer recommendation (who often get a kickback).
The boiler temperature displayed is normally the primary water ie. not the domestic hot water temperature...but if it's cutting out at high temperature (rather than modulating down) it does sound like there are boiler problems...the favorite being the elbow connection to the primary heat exchanger being full of debris and blocked hoses.

 

[BlueLoo]

It's a combi condensating boiler. Connected to DHW and to UFH which is just plastic yes. No rads. Only new copper piping from the boiler to the mainfold. No external pump. There is fresh water for DHW but that goes through the plate heat exchanger, not the main one. They are saying the main one is clogged where the central heating water is circulating.

Commissioned 5y ago and filled with mains water. Treatment unknown as boiler installer retired and is unreachable. No water test. But was partially flushed previous services and water was quite dirty looking. Some black metal pieces like oxide floating around.

I hear you mate, maybe you wanna pop over the pond and take a look
I'm just so frustrated with Viessmann -- all they do is say to call up their authorized service partners. We called 30 and managed to get 2 to eventually come out. Viessmann will not take back any installed parts even if installed by their authorized service partners. Just out of warranty too.

I'd be looking for an actual boiler engineer (not a "plumber") (like yer man below) and binning the OEM techs off. Followed up by a stiffly worded letter to the OEM demanding answers.

 

[Dr911t]

The boiler temperature displayed is normally the primary water ie. not the domestic hot water temperature...but if it's cutting out at high temperature (rather than modulating down) it does sound like there are boiler problems...the favorite being the elbow connection to the primary heat exchanger being full of debris and blocked hoses.

They ran for 2h a Rothenberger pump with acid through the flow/return of the boiler.. quite a bit of yellowish limescale came out. Thing had crazy pressure. I can't imagine anything else being left in the heat exchanger or boiler after that.... but apparently still calcified.

I'd be looking for an actual boiler engineer (not a "plumber") (like yer man below) and binning the OEM techs off. Followed up by a stiffly worded letter to the OEM demanding answers.

Viessmann said due to 'poor heating water quality' it can happen.

 

[Dr911t]

Any ideas what I should do at this point?

* find yet another Viessmann service partner to come and look and pay the call out fee to get an additional opinion
* agree to replace the heat exchanger and hoses €1200+... and pray it's the actual problem as "no return policy on the HX" and if that doesn't work...
* buy a new boiler + install @ at least double the cost of the HX replacement, try to sell the old one for parts to make up some of the $ spent on the part replacement.

What worries me about the heat exchanger suggestion is the strange bubbling noise behind the pump, maybe due to the alleged blocked heat exchanger some water is flowing backward or bubbles somehow making this noise? I'm worried it could also be something with the AquaBloc which is all one big (expensive as usual) piece on the Viessmann which causes some obstruction or problem with circulation.

 

[JCK1]

Well it was a step-by-step replacement.. maybe it's this, maybe it's that. Two Viessmann authorized techs. Viessmann said probably blocked heat exchanger causing the blockage.
Due to calcifying and improper heating water used. Apparently the installer filled it with tap mains without adding any inhibitor and it's been running like that for 4 heating seasons.

Viessmann installation manuals do not require the use of inhibitor to be added to filling water . If you use inhibitor they blame it for causing blockages hot plate heat exchanger. Viessmann installation manuals also allow potable water to be used for filling . The exception would be if you are using your own well water for supply. I suggest down load the manual for your model and check the wording on water quality .

 

[BlueLoo]

*makes mental note to never buy a viessman boiler....*