Viessmann Vitodens 100-w trouble maintaining central heating temp

[Deleted member 123817]

Inchrease each loop flowrate to 2 LPM and see how it goes,

 

[dr911t]

You could of bought a new boiler by now at them costs you would still have to carry out a flush but no that’s not the right way to fault find just throw parts at it

That's the stage I'm getting at bit by bit. I previously lived in warmer climates where electric or HVAC was enough. Gas boilers are new to me.
First the tech came and said it's the plate heat exchanger, replaced that.. didn't help. Let's add some ADEY chemical in the whole system to clear it out.
Then they came back and said well it's probably the pump since there's still no flow. Replaced that... boiler operation was the same.
Then they said it's scale/debris in the heat exchanger so let's do an acid pressure clean, so we did that and boiler operation was the same.
You can see how we go to this but at which point should I have put my foot down and said enough part replacement, new boiler time. A new boiler plus install is not €1000 btw.

 

[dr911t]

Inchrease each loop flowrate to 2 LPM and see how it goes,

all loops are fully open and only getting 1L/min not matter how many thermostats are open or closed.

 

[Deleted member 123817]

Is there a automatic bypass valve (ABV) installed. Some boilers also have a adjustable internal bypass,

 

[dr911t]

Is there a automatic bypass valve (ABV) installed. Some boilers also have a adjustable internal bypass,

No ABV, and I'm not aware of the Viessmann 100-W having an adjustable internal bypass either.

 

[king of pipes]

I'd be very surprised if the boilers main heat exchanger is blocked it's water ways are huge, as said before it's a lack of circulation the boilers pump isn't man enough you need a system pump in my view . Kop

 

[dr911t]

I'd be very surprised if the boilers main heat exchanger is blocked it's water ways are huge, as said before it's a lack of circulation the boilers pump isn't man enough you need a system pump in my view . Kop

The tech kinda blew air through the flow and said it's not getting through to the return easily hence the diagnosis of a blocked heat exchanger causing lack of circulation.

@king of pipes - me too. the tech ran a high pressure pump with and acid solution through the flow and return of the boiler for 2 hours. Quite a bit of yellowish lime scale came out but I'm just surprised the boiler behaves the same (not better not worse) right after this procedure.We are stumped at what is causing lack of circulation, the system was running fine for 4 heating seasons. The original internal Grundfos UPM3 15-75 was just replaced a few days ago before the chemical flush.

 

[Deleted member 123817]

Is there a HX pressure loss chart available for this boiler, that pump should give a 6m head for almost double that flow rate. Also if another pump is installed then might need to be done with TMV/circulating pump and increase the boiler flow temp to say 65C, the boiler circ pump will then only need to supply 30 to 50% of the total circulating flow rate required?

 

[dr911t]

Is there a HX pressure loss chart available for this boiler, that pump should give a 6m head for almost double that flow rate. Also if another pump is installed then might need to be done with TMV/circulating pump and increase the boiler flow temp to say 65C, the boiler circ pump will then only need to supply 30 to 50% of the total circulating flow rate required?

The heating side works continuously without short cycling at boiler flow temp of 50+C return is about 30C.. flow-rate 1L/min.
Anything under that short cycles as boiler temp overshoots.

Maybe here on page 9? https://viessmanndirect.co.uk/files...a6dd00a6c20c/B1HA_B1KA_111-WTechGuide (1).pdf
Internal pump was suspected faulty and replaced with new original Viessmann Grundfos UPM3 15-75 so the same pump specs.

 

[Deleted member 123817]

The boiler should be delivering 12.5Kw at a dT of 20C & 1 LPM.
The plump at 100% speed is a 6.8M.
Assuming 100M of 12mm piping/loop then the residual pump head available is 5.3M and the pipe line losses - 1,5M allowng 20% extra. You should have no problem in increasing the flow rate to at least 1.5LP. It does state "Upper operational limit" and shows a max of 2M head so maybe enquire re this.

 

[Deleted member 123817]

1 LPM or 9LPM for 9 loops

 

[ShaunCorbs]

1 LPM or 9LPM for 9 loops

Jon please use your original account

 

[Deleted member 123817]

Can someone delete the "johntheo" account ?

 

[John.g]

That "upper operational limit is only the pump end of curve conditions so as the pump is new it does point to a restriction in the Hx or else the loops are full of sludge. You may have to prove both clear .

 

[dr911t]

That "upper operational limit is only the pump end of curve conditions so as the pump is new it does point to a restriction in the Hx or else the loops are full of sludge. You may have to prove both clear .

No way to increase flow really as pump speed is controlled by boiler and all loops are fully open. Viessmann tech suspects calcified main heat exchanger due to limescale buildup but theory doesn't explain boiler noise nor still fluctuating tap temp with brand new plate heat exchanger.

I'm leaning toward these pieces of magnetite floating around the circuits causing blockages.
There was black oxide in the old plate heat exchanger so that was cleaned out once but possibly coming from boiler parts corrosion as we have no rads? Thinking to install a Magnaclean or Fernox TF1 or equivalent on the return hopefully it picks up whatever is lying around.

 

[John.g]

If you are handy yourself, maybe connect mains hose to UFH manifold with return disconnected, you will then get a feel for head required to give a flow rate of 1LPM/Loop by cracking open the mains.
You said originally no problems with DHW on old Hx but now some problems with new HX?

 

[dr911t]

If you are handy yourself, maybe connect mains hose to UFH manifold with return disconnected, you will then get a feel for head required to give a flow rate of 1LPM/Loop by cracking open the mains.
You said originally no problems with DHW on old Hx but now some problems with new HX?

Will try.
New circulation pump inside the Vitodens had zero improvement or aggravation of the symptoms. Same low flow rate, same short cycling overshooting of heating temp on lower settings and sometimes luke warm/hot at the DHW taps/shower. Funny metallic gurgling noise from back of pump (both old and now) when boiler is heating but when also idle with pump operational.

Thinking hoses are flaking and constantly obstructing the plate HE, main HE and pump. Possibly in the UFH loops as well.

 

[dr911t]

@John.g - I aired every UFH loop via tap mains pressure and it was ridiculous how low of a head pressure was required for 1L/m! At full blast the gauges were flat down at 4L/min. So it's definitely a circulation problem. Although some of the loops had quite a bit of air in them, even after the slighty tedious work to refill them all and air them one by one, the problem is the same and the boiler behaves identical. Maybe the floor heating has better coverage and more even heating. Definitely a circulation issue, likely boiler side as no blockages in the UFH.

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.

 

[John.g]

Maybe try and figure something out from the DHW (combi?) side, set the boiler HW setting to 3 or4? then open a hot tap fully or even two, measure these flow rate(s) and measure the DHW temp, see if you can can read off the boiler flow&return temps or just the flow temp if only one available, may be able to figure/confirm something from these readings.

 

[dr911t]

Maybe try and figure something out from the DHW (combi?) side, set the boiler HW setting to 3 or4? then open a hot tap fully or even two, measure these flow rate(s) and measure the DHW temp, see if you can can read off the boiler flow&return temps or just the flow temp if only one available, may be able to figure/confirm something from these readings.

DHW Rotary Knob Setting: 4
Hot water tap on full: 10.25L/min
Hot water temp: 40C
Boiler temp: 65-80C

Heating Rotary Knob Setting: Between 4 & 5
Heating flow: 47C
Heating return: 27.5C
Boiler temp: 49-50C
Manifold flow meters: ~1L/min flow meters open fully - all thermostats on, 9 loops.

After turning off the hot water, if I put one hand on the top of the heating flow pipe coming from the boiler and the second hand 1 meter lower, I can feel that the heated water comes through very slowly.

Attached is a recording of the strange noise behind the circulation pump inside the boiler coming somewhere from the Aquablock, behind the pump.
-no water leak or any air from airvent nor the pressure release valve
-system and boiler were recently vented.
-pump is a Grundfos UPM3 15-75. Replaced recently as was the suspect problem, however boiler behavior and noise same as with original 4 year old pump.
-noise reduces in intensity but does not go away after a few moments when pump circulating at lower power in central heating mode.

 

[king of pipes]

It does sound dodgy the only way to find out is strip it out which will need a engineer with a spare pump , as I've said before in my opinion you need a external pump on the heating manifold to push the heating water through the heating loops and back to the boiler , you haven't posted any pictures of your system as requested so we're all stabbing in the dark really.

 

[John.g]

Certainly sounds like a bag of nails and metallic like noise.

From DHW tests the boiler output was 21.5kw (assuming 10c mains) difficult to say what the primary flowrate was but would estimate ~ 10 LPM, what is a bit strange is the variation in boiler temperature, 65C/80C, I would have thought that the boiler would just modulate down to maintain that 21.5kw, did you notice if the boiler ran continuously during this test or was it cycling?, if so then one would expect DHW temp fluctuations as well.
Maybe just repeat this test sometime with DHW setting to max, I would expect the boiler to run continuously as the DHW heating demand is then ~ 36kw, don't know what your boiler output is.

From heating tests the boiler output was 13.8kw at a flowrate of 9LPM.

 

[dr911t]

@king of pipes Here are the photos of the installation. I am aware it is quite a hack job - not done clean and well. Looking back I should have done more research on the installer and asked why no mixer valve, external circulation pump, pressure and temp gauges were installed, which inhibitor or water treatment they used for the fill and asked to do a neat organization of cables and floor. At least I know more now about it for the next project... Live and learn

RE: external pump... what i'm wondering is why it worked 'well' for 4-5 years with decent flow rates, no short cycling, ok steady temperature control

 

[king of pipes]

I can't answer that but what I can say is if you look at my first ever post answering you there a picture of how it should be done ? , a small low loss header with a separate pump fitted would also do the job on your existing set up look at the Viessmann installation guide it may give you a better understanding . Kop

 

[John.g]

Is that the system with the manifold circ pump and where you run the boiler at say 60/65C and UFH at 35/35C which reduces the primary flow rate substantially?. Your post #23.