Another Viessmann 100 problem

[gasned123]

Hi all,

I have installed 2 Viessmann boilers this year. 1st the older 100 heat only compact model. And now the new larger 100W combi version.

After 12 months the compact 100 has only had the F4 problem which was fixed by a new black spark generator.

The newer 100W is having a different kind of problem. After having complaints that the heat wasn't hot enough I turned to the crappy little plug-in digital timer which took me a while to figure out. I managed to put the heating and water on almost 24 hours as there is not room stat however each rad has a TRV. At first I thought it just needed to be setup.

I put the boiler into Comfort mode as well to make sure that Hot water was almost instant. However the problem is with the heating. After leaving the rotary dial on max 6, the burner ignites, reaches 85 Degrees very quickly then the burner cuts out. The display then shows the temp dropping down to 51 degrees then the burner comes on again. This process continues however the heat from the rads is not good enough. We are talking about a 35kw system with 4 rads. I am trying to diagnose the problem and surly thinking that on the max setting the water temp should not have to drop down to 50 before igniting again. Either I have a faulty pump which is making a slightly louder noise but nothing to worrying or another type of fault. I am not getting no errors and the whole system seems fine. Running at 1.5 bar cold, and upto 2 bar while on. No air locks, good pressure just the problem with the heat not being hot enough.

I have rung the tech number at Viessmann but this miserable person keeps telling me he doesn't know anything and that he is sick of the company.

Not very promising.

Can anyone give me any insight?

Cheers

Darren - Central London

 

[JohnD]

I am a householder. I have a 100 Compact (24kW output). Mine runs up to the temp set (I have put stickers on the knob for 60C, 70C and max 80C) and it runs up to that heat, then stops firing until it has cooled down by about 20C from the set temp.

However, mine modulates down from 5 bars flame (very rare) to 4 to 3 to 2 as the heating syst warms up, so it is very slow to reach the set temp, because the nearer it gets, the smaller the flame is. I have 15kW of radiators, and on a cold day, at start up, the boiler runs quite hard until the house is warm, then it runs intermittently as load is less. A boiler stat setting of 70C is plenty but in recent very cold periods I set it to 80 to warm the house up faster from cold. The manufacturer's suggested setting is at 60C which was OK during autumn.

My radiators are quite big so it warms up the house faster from cold, then the TRVs throttle them down. The sytem contains about 100 litres of water so obviously it take a while for the boiler to bring that from cold up to 70C or 80C

Once the house is warm and some of the TRVs have shut, it obviously brings the system water up to temp much faster so it spends less time firing. You say your one has only 4 rads which is not going to keep the boiler very busy. Presumably a very small flat? What is the output of the rads, and how does that compare to the heat required by the rooms? What is the temperature of the radiators?

The only time I had mine short-cycling was on hw cylinder only when the cylinder was near the temp of the primary and it could not absorb much heat. I had to turn up the pump a bit which helped, and increased the differential between boiler stat and cyl stat. This will not apply on your combi, but is it modulating down?

p.s. I am very surprised to hear you do not have a roomstat What were the qualifications of the person who installed it?

24hour running and no room stat is not going to be very economical.

You say every rad has a TRV so the boiler is bound to spend some of its time firing up with nowhere for the heat to go

 

[Razor900]

there is not room stat however each rad has a TRV.

We are talking about a 35kw system with 4 rads.

I hope theres some misstatements there!

 

[gasacs]

If you think the boiler is faulty contact the manufacturer they come with a standard 3 year warranty and if the installer have been on the course it is 5 years.

 

[JohnD]

Another Viessmann 100 problem

but with TRVs on all rads, and no room stat, and boiler getting hot but rooms not warm enough, it sounds to me like another design problem.

It will be interesting to find out what the radiator sizes are and how they compare to room heat losses, as well as how hot the rads get.

 

[gasned123]

I just purchased the Vitoroll 100 UTD RF plugged it into X7 on the board.

Setup the temp to 30 degress on the room stat still the same problem.

I think the pump is fine as the Rads are getting hot however they are not staying hot.

Im pretty sure its a faulty control unit of some sort on the boiler.

Even without the Room stat, the TRV will give the system some degree of regualtion. If the flat (which is only a small 2 bed with 4 normal size rad and a bathroom towel rad) is at approx 15 degress the boiler should stay fired regardless of the room stat or not.

I have read through the instructions of the Vitocroll and I have to say its not the most straight forward controller. But any way its a problem with the electronics on this V100

Ringing Viessmman all day yesterday and today with no luck, and now Im stuck all weekend and most probabley next week with out any heating.

I think its ridiculous that they are closed on Sat....

 

[htgeng]

p.s. I am very surprised to hear you do not have a roomstat What were the qualifications of the person who installed it?

Unless I misread, he was the person who installed it

 

[gasned123]

Indeed I installed the boiler, but didnt bother at the time with a room stat.

 

[JohnD]

You say your one has only 4 rads which is not going to keep the boiler very busy. Presumably a very small flat? What is the output of the rads, and how does that compare to the heat required by the rooms? What is the temperature of the radiators?

Any response?

 

[superdupergasman]

Why not range rate it down... tells you how to reduce the CH rate if there is a small load on the system in the Manf instructions using POT A on the PCB.

If its 30kw firing at full power with 4 rads it will get up to heat super fast!

Make sure the rad valves are open for max flow through the rads.

 

[gasned123]

I didn't actually think of that, I will try to lower it to maybe 3-4 on the rotary switch and see if it maintains the temp. I think if the boiler could stay at 60 deg and stay burning it will be better the current situation.

Does any one have any experience with the Viessmann service people?

Will they come to the property quite quickly?

 

[gasacs]

in our area they are usually on the job within 48 hours if requested by an RGI if you are not an RGI am not sure if they will come out under warranty and if they do be prepared for them to point out all faults (if any) within the installation.

 

[JohnD]

and how big are the radiators and the rooms?

 

[simond]

Viessmann use a lot of service agents for warranty and if the install is not up to standard (if service tech suspects its not up to standard) you can expect an argument.

 

[gasned123]

The total sq ft of the flat is 650, and the rads are approx 60 X110

I turned the dials down didnt do anything, same problem.

However I managed to get the boiler into SERV mode. DHW is on the spot and CH is now on 6. The display shows ECO and SERV.

Now the boiler is going upto max temp dropping to 80 them coming on again and mainting the temp. It did this for about 30 minutes.

The SERV then went off, and now its doing the same thing again my going up 85 deg, burner goes off, then waits to go down to 50 degrees before the burner comes on again.

Does any one now how to get a SERV guide maybe I have put the boiler into some sort of setting mode. I have tried a cold reboot of the boiler but same problem.

All the downloads from the Viessmann site are only basic and do not show the SERV functionsss