02-02-2012, 02:21 PM
Hi Ed,
Having just re-read the previous thread, a lot of good advice has already been given there. In summary, I'd say the following:
I've just fitted a Viessmann. A very easy DIY job (apart from the gas, obviously). I went for the Vitodens 200 System Boiler - unless you're very short for space, I wouldn't recommend the 100 as that is a "dumbed down" model for the UK market - it had some reliability issues initially as well (long since solved, but you'll find no shortage of people complaining in the forums - just check the dates of the posts, and don't let them put you off the brand).
The system boiler contains the pump and diverter valve, so has 4 pipes; 2 for heating flow/return and 2 for water flow/return. You can keep your existing diverter valves and use the boiler in 2-pipe mode if you wish, but you would be mad to do so (explained later).
Most condensing boilers on the market still use aluminium heat exchangers. This is bad! See my previous posts.
You might have trouble with the flue. There are new regulations that state the flue has to be accessible for inspection at all points where there are joins. This will mean adding hatches or similar in the chimney stack. Not good. Have a look at Jeff Howell's column on the Telegraph website, where this has been discussed previously. I'd find a way to run it horizontally if humanly possible. Don't forget that actually it needs to slope down slightly back to the boiler...
I've also read somewhere that boiler cupboards do need ventilation, even when the boiler is room-sealed. I haven't had a chance to investigate this fully yet - apparently it's a new regulation - but if true, it's a real pain. Ventilating to the outside will surely bring in enough cold air to undermine the overall efficiency of the installation. Certainly, manufactures state that ventilation is not required, but regs override manufacturers guidelines here... I would welcome clarification on this if anyone knows any more...
While on the subject of efficiency, I wouldn't worry about the published figures on the SEBUK site. What's the difference between 90 and 91% when you're coming from 55-60%? Instead, it's far better to focus on the TCO, which means avoiding boilers that will break down and wipe away any savings on your gas bill. Also, these figures don't include the potential savings from Weather Compensation.
Weather Compensation: I have it, and I am still really, really impressed by it. IMHO, you would be mad to ignore it. Not only does it improve the comfort, it also saves on the bills. I couldn't work out how it would even begin to work, and really, I went out on a limb, based on advice from a trusted friend. But, to say I'm very pleased would be a massive understatement.
There is no room thermostat. The boiler adjusts the flow temperature based on the outside temperature. It does all it can to maintain a constant indoor temperature in the face of varying outside temperatures, while avoiding cycling. It's very smart. If the boiler has just spend 10 minutes heating the water (DHW priority), it uses an increased flow temperature for the heating for a short period, just to compensate for that short period of cooling. There is definitely an element of "fuzzy logic" or similar, but whatever it is, it works well.
Weather Compensation is mandatory in some parts of Europe. Viessmann have been doing this for years, and know what they are doing. Worcester-Bosch have only just started, and they are playing catch-up. And they still use aluminium for the heat exchangers. Although I have a lot of Bosch tools and white goods, I wouldn't choose one of their boilers.
WC maintains comfort by running the boiler continuously, but at a very low flow temperature. This alone saves a lot of fuel, and is frequently advocated by Jeff Howell (his correspondents either tell him he's mad, or tell him that it makes an amazing difference to the bills - clearly the former group haven't tried it!). Because the boiler can modulate down to a quarter of its rated output, it means that in temperate weather, it runs at low power rather than cycling on and off. The radiators aren't dangerously hot, and the fabric of the house is kept drier - especially important for old houses.
DHW priority is essential - the boiler can't run at two temperatures. When heating water, it ramps up to 70C or so. When heating, the WC decided the best flow temperature. That's why you'd be mad to use it in 2-pipe mode. If so, you'd have to choose a flow temperature hot enough to heat the water, which would be too hot for heating - causing cycling.
The Vitodens 200 supports zoning and solar. I haven't needed to investigate these options, but I'd recommend you downloaded the guide and had a good look. The control system is very advanced (yet very user-friendly) and will almost certainly do a better job of zoning than any 3rd party or (with the greatest of respect) DIY solution. Our house is too small to zone, plus as it's a Victorian terrace with solid walls I'd prefer to keep it warm and dry throughout anyway - but I am interested in solar for the hot water. I'd buy a new cylinder with the extra coil - how do you propose adding another coil to yours? Can you cut them open and solder them back together? These things have a finite life anyway - in fact I was fearing the worst when attempting to replace the pipes going to the coil, but so-far so good!
You should consider changing to a sealed system - I think that many manufacturers expect/mandate that these days. The trouble with a header tank is that it lets in oxygen. The expansion vessel is normally built into the boiler - normally behind everything else so that when the diaphragm fails, most people simply fit an external one!
In terms of warranty, the Viessmann comes with 3 years if you (or a regular contractor) fits it, and 5 years if it's fitted by someone who has attended the training - which I believe is free, or very cheap. The stainless steel heat exchanger is guaranteed for 10 years. Looking very, very critically at mine, I couldn't see a single component that would be difficult to replace it the need arises. The expansion vessel is at the side, and comes out after undoing 2 screws.
The boiler wasn't even expensive. Obviously a bit more than a Worcester-Bosch, but well worth it. Investigate PTS, who have branches in many towns and cities. You can download their prices, and you'll find that they give you around 50% off without even asking.
One day I'll start a thread detailing my installation with some pictures, etc, but I hope this gives you something to think about in the meantime...
Mark
Having just re-read the previous thread, a lot of good advice has already been given there. In summary, I'd say the following:
I've just fitted a Viessmann. A very easy DIY job (apart from the gas, obviously). I went for the Vitodens 200 System Boiler - unless you're very short for space, I wouldn't recommend the 100 as that is a "dumbed down" model for the UK market - it had some reliability issues initially as well (long since solved, but you'll find no shortage of people complaining in the forums - just check the dates of the posts, and don't let them put you off the brand).
The system boiler contains the pump and diverter valve, so has 4 pipes; 2 for heating flow/return and 2 for water flow/return. You can keep your existing diverter valves and use the boiler in 2-pipe mode if you wish, but you would be mad to do so (explained later).
Most condensing boilers on the market still use aluminium heat exchangers. This is bad! See my previous posts.
You might have trouble with the flue. There are new regulations that state the flue has to be accessible for inspection at all points where there are joins. This will mean adding hatches or similar in the chimney stack. Not good. Have a look at Jeff Howell's column on the Telegraph website, where this has been discussed previously. I'd find a way to run it horizontally if humanly possible. Don't forget that actually it needs to slope down slightly back to the boiler...
I've also read somewhere that boiler cupboards do need ventilation, even when the boiler is room-sealed. I haven't had a chance to investigate this fully yet - apparently it's a new regulation - but if true, it's a real pain. Ventilating to the outside will surely bring in enough cold air to undermine the overall efficiency of the installation. Certainly, manufactures state that ventilation is not required, but regs override manufacturers guidelines here... I would welcome clarification on this if anyone knows any more...
While on the subject of efficiency, I wouldn't worry about the published figures on the SEBUK site. What's the difference between 90 and 91% when you're coming from 55-60%? Instead, it's far better to focus on the TCO, which means avoiding boilers that will break down and wipe away any savings on your gas bill. Also, these figures don't include the potential savings from Weather Compensation.
Weather Compensation: I have it, and I am still really, really impressed by it. IMHO, you would be mad to ignore it. Not only does it improve the comfort, it also saves on the bills. I couldn't work out how it would even begin to work, and really, I went out on a limb, based on advice from a trusted friend. But, to say I'm very pleased would be a massive understatement.
There is no room thermostat. The boiler adjusts the flow temperature based on the outside temperature. It does all it can to maintain a constant indoor temperature in the face of varying outside temperatures, while avoiding cycling. It's very smart. If the boiler has just spend 10 minutes heating the water (DHW priority), it uses an increased flow temperature for the heating for a short period, just to compensate for that short period of cooling. There is definitely an element of "fuzzy logic" or similar, but whatever it is, it works well.
Weather Compensation is mandatory in some parts of Europe. Viessmann have been doing this for years, and know what they are doing. Worcester-Bosch have only just started, and they are playing catch-up. And they still use aluminium for the heat exchangers. Although I have a lot of Bosch tools and white goods, I wouldn't choose one of their boilers.
WC maintains comfort by running the boiler continuously, but at a very low flow temperature. This alone saves a lot of fuel, and is frequently advocated by Jeff Howell (his correspondents either tell him he's mad, or tell him that it makes an amazing difference to the bills - clearly the former group haven't tried it!). Because the boiler can modulate down to a quarter of its rated output, it means that in temperate weather, it runs at low power rather than cycling on and off. The radiators aren't dangerously hot, and the fabric of the house is kept drier - especially important for old houses.
DHW priority is essential - the boiler can't run at two temperatures. When heating water, it ramps up to 70C or so. When heating, the WC decided the best flow temperature. That's why you'd be mad to use it in 2-pipe mode. If so, you'd have to choose a flow temperature hot enough to heat the water, which would be too hot for heating - causing cycling.
The Vitodens 200 supports zoning and solar. I haven't needed to investigate these options, but I'd recommend you downloaded the guide and had a good look. The control system is very advanced (yet very user-friendly) and will almost certainly do a better job of zoning than any 3rd party or (with the greatest of respect) DIY solution. Our house is too small to zone, plus as it's a Victorian terrace with solid walls I'd prefer to keep it warm and dry throughout anyway - but I am interested in solar for the hot water. I'd buy a new cylinder with the extra coil - how do you propose adding another coil to yours? Can you cut them open and solder them back together? These things have a finite life anyway - in fact I was fearing the worst when attempting to replace the pipes going to the coil, but so-far so good!
You should consider changing to a sealed system - I think that many manufacturers expect/mandate that these days. The trouble with a header tank is that it lets in oxygen. The expansion vessel is normally built into the boiler - normally behind everything else so that when the diaphragm fails, most people simply fit an external one!
In terms of warranty, the Viessmann comes with 3 years if you (or a regular contractor) fits it, and 5 years if it's fitted by someone who has attended the training - which I believe is free, or very cheap. The stainless steel heat exchanger is guaranteed for 10 years. Looking very, very critically at mine, I couldn't see a single component that would be difficult to replace it the need arises. The expansion vessel is at the side, and comes out after undoing 2 screws.
The boiler wasn't even expensive. Obviously a bit more than a Worcester-Bosch, but well worth it. Investigate PTS, who have branches in many towns and cities. You can download their prices, and you'll find that they give you around 50% off without even asking.
One day I'll start a thread detailing my installation with some pictures, etc, but I hope this gives you something to think about in the meantime...
Mark
