Viessmann boilers

[cr0ft]

Gents,

Popping out to look at a Viessmann Vitodens 100-W boiler where the pressure gauge is slowly dropping over 6 months or so to 0.2 bars or so. The boiler keeps working despite this. Does this boiler have a safety cut-out if the pressure drops below the 0.8 bars the manual says it needs?

Am suspecting a faulty pressure gauge but would be good to know if it has a safety cut out or not.

Cheers!

 

[Chalked]

Faulty pressure gauge, probably.

Leak or prv dripping, definitely.

 

[cr0ft]

It's a large system so I'm suspecting there is no external expansion vessel when it needs one. Will update tomorrow! Am surprised the boiler still runs at 0.2 bar though, thought they all cut out around 0.6 bars?

 

[mfgs]

Depends on the boiler. Worcesters don't have a low pressure cut out so will run on 0 bar pressure.

 

[townfanjon]

They will virtualy run on no pressure

 

[cr0ft]

Makes you wonder why they need to be at 1.2 bars or so then??

 

[Chalked]

Stupid to not have a pressure switch! Can burn out the pump and cause all sorts of other probs.

 

[cr0ft]

Gents,

Have just spoken with Viessmann technical today who have confirmed all Vitodens 100-W boilers are fitted with a pressure switch that locks the boiler out if pressure drops below 0.5 bars.

Customer has confirmed pressure gauge is reading 0.2 bars on the front of the boiler today but yet the boiler is still running. No signs of any leaks in their house at all. We installed all the pipework from new 1 year ago and pressure tested it all to 10 bars with no issues.

So to me the fault is either a faulty pressure gauge OR a leak we can't see AND a faulty pressure switch in the 1 year old boiler. Any other possibilities you can think of before I go across there?

 

[markfxy]

prv could be dripping it runs inside the condense pipe so wouldn't be noticed

 

[1Steven]

They are good boilers, has it been top up at all? If its a large system my need bigger vessel.

 

[Scott_D]

Let the pressure off on a drain off. See what happens to the gauge and see if the boiler still works with no pressure

 

[cr0ft]

Well phoned back Viessmann technical whilst at the iob today. This time I spoke to a lady who said there is no pressure switch.. What hope have I got of diagnosing the issue if their own staff don't even know their boilers lol.

 

[c.gas]

all manufacturers are the same, it all depends who you speak to, u ring back 5 mins later and get through to someone else and they give you a bit more/different info. It's the same with gas safe, it just depends who you speak to

 

[mfgs]

Well phoned back Viessmann technical whilst at the iob today. This time I spoke to a lady who said there is no pressure switch.. What hope have I got of diagnosing the issue if their own staff don't even know their boilers lol.

Technical helplines can be useless, or amazing. Just count yourself lucky you haven't had to phone Vokera, they are always so rude! Maybe go old skool and resort to looking in the manual, the wiring diagram will soon tell you if there is a low pressure cut out or not.

 

[Dotty]

Or, if you can wait until Friday week, I'm going on a Viessmann course in Dublin!

 

[cr0ft]

Hi Croppie. If you would be able to ask the question for me that would be brilliant. Will get my head in the manual in the meantime.

 

[ShaunCorbs]

Easy way to tell can't you put a pressure gauge on the filling loop to check that the pressure is right ?

 

[cr0ft]

The lad is phoning me back in a week. I did think of doing that but they all have non-return valves on them so it would have to be a case of removing it from the CH return pipe which means draining the system down. As it's such a slow leak, if it is indeed a leak, I'm going to rule out the condensate/PRV then put a bit of leak sealer in I reckon.

 

[Toxic Ted]

I have just looked through the schematic and can't find any pressure switches and the gauge is capillary so no electrical connections for a switch.

 

[Leo21]

Chuck some Fernox leak sealer in there, job done.

 

[kris]

See that too many times with no allowance for the extra expansion vessel on the bigger properties..

 

[cr0ft]

Why would pressure drop if expansion vessel capacity was undersized (without an associated spike to 3 bars when warming up)?

 

[Leo21]

Why would pressure drop if expansion vessel capacity was undersized (without an associated spike to 3 bars when warming up)?

If it's not big enough, it would spike.

 

[hammers4spanner]

Chuck some Fernox leak sealer in there, job done.

Aint that supposed to be PVA??

 

[tamz]

Aint that supposed to be PVA??

Not much difference imo. I'll shove a half litre of polybond in mine next time it drops and see how it goes 😉