Viessmann boiler failure

[Mark Hennessy]

In fairness, the 100 was always intended to be a cut down model for the UK market, who insist on buying the cheapest thing possible. Viessmann don't have problems selling their "proper" products in Germany, naturally. Early versions of the 100 gained a poor reputation for reliability, but those were sorted before you bought yours. I suspect this problem is just random failure, but annoying nonetheless. Hopefully there's no consequential damage as a result of the leak?

Nice to see that the expansion vessel is also easily accessible on yours. Quite a bit smaller than mine, so as you say, perhaps that's the problem. An additional one might be useful, perhaps... Ours is a 3-bed Victorian terrace. No loft conversion. 9 rads - will be 10 or 11 in the fullness of time. What might contribute to the difference - rather than system size - might be weather compensation, resulting in much lower flow temperatures than yours?

With the 200, the pump is the noisiest thing. And that's mostly the noise of the water moving through the pipes. The fan is only audible with the front cover removed, and that's mostly air noise rather than mechanical noise. There is an occasional clunk from the diverter valve (I think), but overall, I'm very impressed with how quiet they are. Important, because it's in a bedroom. I still haven't got around to building the cupboard around it - that's almost the next task in this 5 year (and counting!) restoration project. I bet that once the acoustically treated cupboard has been done, it'll be totally inaudible.

Any word from Viessmann about the warranty, etc? Any idea about that'll cost as a replacement if you have to pay?

[ppppenguin]

AFAIK a Viessman fitter will come tomorrow and fix it at no charge to me.

The only significant damage is to the ktichen ceiling. A small area will need a bit of filling, stainblock paint and repainting. Not serious.

Mark, your 200 seems really quiet. On mine when it's running at full chat the fan is definitely noisy. Or it might be the burner. Can't tell. Not enough to be annoying in its cupboard on the landing but would be horrible in a bedroom.

[Mark Hennessy]

That sounds like a result

[Radio Fixer]

I wouldn't go anywhere near a pressurised system in this 70s house !!  My neighbour did and it would never hold it.  Of course like me he had no leaks.  Ended up having the house re-plumbed 

Gary

[Murphyv310]

Ours is pressurised, a bit of a wing and a prayer though as the incoming pressure is 0.8bar, if I'm lucky it may reach 1bar during the night. Fortunately the system holds water very well and it's well over two years before its dropping to 0.6bar. Topping up the pressure takes an age and I now have made up a home made filling device with a reservoir tank of water and a tyre valve to attach a footpump to do it. I'll be waiting till the pressure drops before I test it though!

[ppppenguin]

Mine holds pressure very nicely thankyou. Probably top up less than annually.

Viessmann guy has been and fixed it. No trouble at all. He also showed me why it had failed. A lot of flakes of black iron oxide in the pipe, causing scour on the bend where it failed. I have no idea why I have so much muck in the system. It was well flushed (not power flush, just good old mains pressure directed via each rad in turn and in both directions before installing new boiler), has a Magnabooster 2 and plenty of inhibitor.

The Magnabooster really ought to trap out the stuff on its way round. I suppose I should be considering a power flush, or possibly an acid clean.

After doing the work he checked burner pressure and flue gas. He said the FGA was exceptionally good for a 5 year old boiler.

PS: If your system loses pressure consider using this: http://www.fernox.com/products/water+tre...+sealer+f4

[boater sam]

If a modern boiler of any type, combi, or 'system', is to be fitted to an old system an acid flush is a necessity.  A so called power flush is only a quicker way of cleaning out the debris, repeated washing through in both directions achieves the same result provided the debris is loosened by an acid soak first.
We used to leave it to soak at least overnight followed by repeated hot and cold fresh water flush until the water is crystal clear, as clear as what comes out of the tap!
We always acid flushed even new systems, new radiators are not clean inside and any metallic pipework will be contaminated.

I think you have done well not to be charged for the repair, many manufacturers would have charged you if there was any debris in the water.

The expansion vessel is charged with dry nitrogen, not air. Repressurising with compressed air does shorten the life. The working volume should not be less than 5% of the system total volume otherwise over pressure will result when the system is at maximum temperature.

Using an anti corrosion additive is mandatory,  using a leak sealer is a bit suspect as it introduces contamination and will not seal worn radiator valves or lockshields. Systems that lose pressure regularly need attention, not just frequent topping up. With good quality valves and careful assembly there should be no leaks. We used to test to 5 bar.

I don't think there is a boiler manufacturer who will guarantee an open system with header tank on a sealed system boiler.

[Mark Hennessy]

That was quick!

Good to hear your system is well-sealed. I seem to remember a thread a couple of years back where you had a minor leak, but can't remember if it was ever resolved? But then, I can't remember what I was doing yesterday, so that might be an invented memory...

I think we've talked about that Magnaboost filter before. Whenever I purge it, the water comes out disappointingly clean. However, when I removed an old radiator last year, I was amazed at the amount of black muck that eventually came out when I tipped it up to pour out the last of the liquid. I guess the sludge accumulates at the bottom of the rads - below the level of the inlet/outlet connections - and only relatively small amounts of it are actually moving around the system.

By the time I've finished, I will have replaced all the rads in the house. Though at the current pace, that'll be sometime around 2035. I wonder how many new boilers I'll get through in that time

Trev, 0.8 bar is terrible. But surprisingly, the minimum they have to provide is only 0.7 bar. Dread to think what we have here, but I have no problem getting the system up to 3 bar before chickening out. Presumably your shower is gravity fed? Still, I suppose low pressure is kinder on tap washers

I don't know what the minimum pressure would be for the Viessmann boiler - as I mentioned earlier, I don't know if it has a low-pressure detection switch. If it does, it'll be part of the pressure gauge, as I'm 99% sure there isn't a separate sensor in the flow/return pipework. I don't recall the manual mentioning it, but it's been 5 years since I last studied it. Luckily our system is relatively modern - the rads and pipework were installed in the late '90s - and it was a sealed system at that point. Sealed systems can be a nightmare for older systems, but generally, I think they're a better bet.

Anyway, excellent service from Viessmann

[ppppenguin]

At 3 bar you'll often have the overpressure valve opening. Happened once while I was repressurising a friend's system after changing a rad. Made a horrible hammering noise. Apparently the overpressure valve opens so rarely that sometimes it won't reseat properly after opening, thus giving a pressure loss problem.

All boilers with a pressure gauge will have an underpressure detector that will stop it firing. Typically at 0.25 bar.

Must get another can of Sentinel X100 inhibitor. I know I didn't lose much water (a little goes a long when when it's flooding!) but it never hurts to keep up the inhibitor level.

[boater sam]

Very true Jeffrey!  Hammering safety valves, terrifying.  And we used to find many discharging inside in the early days, hate to think what would be the result of a blow off.

They used to be a source of leaks until the quality improved. The other common leak was the non return valve on the fill loop leaking back, and often not disconnected as it is supposed to be, leading to hose failure.

Obviously when we pressure tested at 5 bar, the boiler was isolated otherwise we would have lifted the safety and done the expansion vessel no good, it was just the pipework. valves and radiators we pressurised to ensure that there were no oozing unions or valves.

The biggest sealed system we installed had 98 radiators, 360,000 Btu's. in a seniors care home.  All on push-fit plastic, no hot working allowed as the building was part occupied, and many reused radiators. The only leak we had was a 28mm elbow in a basement that had no "O" ring in one end! 
Just as well because the floors were all sheeted and carpeted before we filled up!