Viessmann boiler doesn't like sunshine

[Yardman]

I have a Viessmann Vitodens 200 WB2 6-24 combi boiler (not included in the recall) that will loses boiler water pressure every time the sun comes out and the outside air temp rises above 50 F. The Viessmann heats our radiant floor system and provides domestic hot water to a storage tank. When it is cloudy and cool, the pressure maintains at 10-12 lbs. and the boiler contently fires for days. As soon as the sun comes out, and air temps rise, you can watch the boiler water pressure meter drop to 4-6 lbs. over a few hours, and the boiler will not fire as it requires a min. of 8 lbs. of pressure. I have to manually boost the water pressure to 10-14 lbs. using the incoming Taco adjustable pressure regulator, and then keep an eye on it until sunset when it works fine again. I replaced the boiler water pressure sensing switch last fall when it failed and would not allow the boiler to fire; that was when the storage tank and recirculating pumps were added to the system. The Viessmann outdoor sensor is mounted on the south side of the house in the sun, contrary to Viessmann’s directions, but it has always worked to the system’s satisfaction. To experiment, I have covered the sensor to mimic it being on the shaded north side of the house but there has been no change. Viessmann technical says there are no components or software in their product that would cause the boiler to lose pressure in this way. There are no leaks that I can find anywhere. The incoming water bladder tank has air pressure. Our house main line in has 150 lbs. pressure adjusted down to 50 lbs. line pressure. This problem never happened until the storage tank and pumps were added. My heating contractor is stumped and no one in my area speaks Viessmann. Any thoughts?

 

[PEDANTICVINDICTIVEMAN]

Can you isolate the storage tanks temporarily to see if it behaves.

 

[D_Hailsham]

I see you are in the USA. This is a UK based forum and we do things differently this side of the pond.

You may find more appropriate help is you used a US based forum such as Heating Help.

 

[Yardman]

Can you isolate the storage tanks temporarily to see if it behaves.

I'm sure the storage tank can be isolated. Why would the tank be causing the boiler to lose pressure when the outdoor temps rise?

 

[Yardman]

I see you are in the USA. This is a UK based forum and we do things differently this side of the pond.

You may find more appropriate help is you used a US based forum such as Heating Help.

Thanks. It seemed like this was a U.K. forum but I am willing to listen to anyone who can help me puzzle this out since Viessmann is not widely used in the U.S.

 

[Alfredo]

If its losing pressure then that water is going somewhere, either out through the pressure relief valve, or maybe its siphoning away somewhere. It really needs to be 'caught in the act'. Maybe the pressure vessel doesn't have enough capacity to cope with the overall expansion in the system when the sun gets hot, and some gets squirted out that way.

I am rather shooting blindfold here as its not one I have come across. Viessmann is good kit, not been in the UK so very long either, but is making a good impression. Dare I mention German ruthless efficiency..with my tongue in my cheek

Alf

 

[Happyplumber]

Veissmann have been in the uk for donkeys years and are massive in the commercial section

In America they like you to use registered plumbers try and find that bloke who mclain and palin were touting he may now be registered!

 

[Alfredo]

Oh alright then, but I don't do commercial and worked most of my time on Housing Assoc. stock, where they were a rarity. Can't say I saw one in a private house until about five years ago, but I know they are long established as a company.

Alf