Vaillant Ecomax 635 F.25 and no water pressure

Every two weeks or so when waking up in the morning there is no hot water and no heating. Boiler shows F.25 and the water pressure is 0. So the pressure must be getting too high which causes the PRV to open.

This also seems to start to happen every year when the colder weather comes.

Last month we actually had the PRV replaced as it had stuck open and was kaput after the above had happened. I asked the engineer Homeserve sent to check the expansion vessel as he had not done so a month earlier during the annual service and it needed re-pressurising, so he did this.

http://uk.answers.yahoo.com/question/index?qid=20101026073413AA16dge

In the above Yahoo link a Vaillant enginner says "firstly boilers fixed to cold garage walls, naturally deflate twice as much/quicker than in warmer kitchen mounted boilers. second the masive winter we had last year will have deflated your vessel more than in a normal winter."

Is this correct? How does being in a colder enviroment affect the expansion vessel? Our boiler is in the garage fixed to the rear wall so could this be part of the problem?

Secondly what pressure should the expansion vessel be at and can it be re-pressurised with boiler turned off with water in the system or does the system need to be drained first?

Would the expansion vessel only need replacing if water came out the valve when depressed?

Thanks.

Thanks. Does anyone know the answer to the below.

http://uk.answers.yahoo.com/question/index?qid=20101026073413AA16dge

In the above Yahoo link a Vaillant enginner says "firstly boilers fixed to cold garage walls, naturally deflate twice as much/quicker than in warmer kitchen mounted boilers. second the masive winter we had last year will have deflated your vessel more than in a normal winter."

Is this correct? How does being in a colder enviroment affect the expansion vessel? Our boiler is in the garage fixed to the rear wall so could this be part of the problem?

Someone who has to work for Homeserve either thinks its fun to come out with adsurb statements for fun or perhaps even believes it.

Next time ask what degree he has got!

Tony

The 10 litre expansion vessel is grossly undersized for most of these vaillants , install an additional 25/35 litre vessel job done.

I will look into that thanks. So will they just remove the internal expansion vessel, install an external one which will conect to where the internal one is connected or does the boiler have some sort of provision for an external expansion vessel?

How much roughly should I be looking at to have one installed? Any recommendation for a particular make / type of external expansion vessel?

Thanks.

Gas wizard havin a bit of fun I think, I never had any issues with exp vessels on these 10 l is fine

I have fitted an extra exp vessel only twice. Both on massive houses with around 25 large rads fitted to both and between 30kw and 37Kw heat requirements.

The house is 3 storeys, 11 rads. Garage is in the garden detached from the house and the boiler and megaflo etc are in the garage. We do tend to have the heater on alot as the downstairs is always colder and takes longer to heat and a family member with a chronic illness is always cold so we tend to keep the house at a more comfortable temperature.

There is no air in the system. The cold pressure is just above 1 bar and pressure remains constant so no leaking filling loop. TBH we just want to sort it out once and for all.

We do have to have the expansion vessel re pressurised every year at least. If fitting a larger external vessel is going to stop this happening then that seems the best solution?

10 litre EV is only good for systems 100 litres and smaller (1 bar) , total up the system volume for a 35 KW output and you'll find the 10 litre vessel is tooooooooo small. , i could do the maths but i can't be arsed.

Considering the head (3 floors) system pressure would be around 1.5 bar , with a system volume of 100 litres (OP would be more) EV volume would have to be a minimum of 16 litres.

Strange how vaillant use the same size vessel whether a 12 kw or a 37 kw , now in my book that ain't engineering.

What GW is trying to say is that IF you really needed a 35 kW boiler then you would need an additional EXV.

The reality is that with just 11 rads your boiler is massively over rated and the internal EXV is fine!

Many people use a rule of thumb that an average rad is 1.5 kW so that means an 18 kW boiler would probably be enough and more efficient!

Tony




PS that Homeserve fellow saying that makes me wonder if he has emptied all the air out of the EXV in spite or some odd kind of pleasure kink!

Installed 5 radiators into a property that totalled 37kw.

Increasing fill pressure by 50% will require twice as much tank , hence the 1 bar fill pressure versus the 1.5 bar pressure , vaillant size these vessels on a 1 bar static fill pressure.