Central heating boilers (again)

[SteveD]

Many thanks to those ABers who gave very useful advice in answer to my previous question about this same subject.

We have now narrowed our choice down to two installers - one who proposes Vaillant and one who proposes Viessmann.

The one who has quoted for Viessmann very strongly recommends an outside sensor for the central heating system whereas the other one says that not having an outside sensor will be perfectly adequate.

The Viessmann man also suggested that Vaillant use aluminium while Viessman use stainless steel which is much better. I see mention of stainless steel in the Viessman leaflet, but nothing in the Vaillant one.

May I have your comments on these two points, please.

[tezestwing]

Hi Steve I have been following your post with interest
I have also been advised to go for stainless steel if possible but the choice is very narrow
Not sure about the censor?extra cost? Regs require TRVs or Area Stat now so you just set the room temp by them
I have had good reports on the Worcester Range also good on spares ring up local or national outlets and ask how quickly they could deal with a particular model/make I suspect foreign makes may be slow
I have also considered the pros and cons of keeping the indirect hot water cylinder with immersion back up in the event of breakdown for family hot water HTH Tez

[gucciman]

the trouble with the new generation of condensing boilers is that the condensate is acidic so the boiler slowly dissolves itself, hence the use of stainless steel by the high end boiler makers. when we service a condensing boiler and we clean out the condensate trap you can actually see the metal in the bottom of the trap.
(the government pushes the condensing boilers but i wonder what they will say in 50 yrs when all the drains and sewers corrode!)
i honestly dont know anything about viessman boilers as ive never come across one. i dont know how reliable they are and how available the spare parts are. i will ask my old man though when i get chance as he will probably know about them.
i wouldn't let this put you off either a vaillant or worcester though, the corrosion on the modern condensing boilers (theyve been around 20yrs or more believe it or not) isn't too much of a concern as its a slow process and the rest of the components will have packed up long before the heat exchanger.
oh and beware of some installers recommending a particular make as they get generous discounts from the plumbing merchants and makers if they install so many.

[SteveD]

The choice is going to be between Vaillant and Viessmann and the final decision will probably be made based on the way the installer concerned proposes dealing with the radiators which we are going to have fitted. I won't go into this here as it's peculiar to the type of central heating system we have in this house and nothing to do with the brand of boilers.

I should point out that we live in Belgium. Availability of spares etc should not be a problem. Vaillant and Viessmann are German.

Does anyone have any comments about this question of the outside sensor?

http://www.vaillant.co.uk/

http://www.viessmann.co.uk/

[gucciman]

what precisely do you mean by an outside sensor? are you talking about a room thermostat?

[solera]

The outside sensor is probably a frost sensor and is intended as an overide to fire up the boiler in the event of low temperatures, some makes of boilers fit these as standard and others are a chargeable add on, check with your supplier. The Weissman unit is superb and the use of stainless speaks for itself. It can get very cold in your part of the world so ask both of the suppliers the same question.
Best of luck for the future.

[gucciman]

yeah i wasn't sure if he means a froststat or a room stat. most modern boilers have a frost stat built in these days and over in the uk they are only really needed if the boiler is installed in a garage, loft or an outhouse of some sort. cant do any harm i guess if the price is reasonable.
if its a room stat then id definately go for one, makes the heating a lot more controllable and efficient.

[kp nonuts]

A frost stat is normally fitted next to the boiler itself or in the loft.
What would be the point in putting it outside as you would get a false reading when you take into consideration the wind chill factor etc.

[SteveD]

Here is a section from the Viessmann website talking about the function of the outside sensor:


"Vitotronic automatically calculates
the optimum temperature for
living space and boiler water. These
are derived from the values of the
outside temperature and, subject to
individual system design, also from
those of room temperature and
heating water flow temperature.
Naturally it also takes into consideration
the time of day and season of
the year, whilst individually controlling
heating circuit pumps according
to demand."


According to the installer, it makes the whole system operate more efficiently.

It doesn't get any colder here than in south-east England. What Kent gets today, we usually get tomorrow!

[tezestwing]

Steve these sophisticated programmers with optimum heat up times and so called day economy runs and run time delays are just another way of you putting your room stat at a temperature that you are comfortable with and the boiler does the rest when it receives this information like temp control in your car maybe, but when they go wrong no heat and no hot water, possibly in winter HTH Tez

[gucciman]

yeah and i bet they cost a fortune to repair or replace when they go wrong.
right, im back at work today so have asked the old man about viessman boilers. basically he said that for years viessman specialised in industrial heating products and have moved into the domestic heating market. he said that in all the years (48) of working as a gas engineer he has never come across a veissman boiler in someones house, for this reason spare parts may be hard to come by as the parts retailers are not going to stock something they hardly ever sell, would probably have to be special order. (bear in mind this is the uk, belgium may be different)
he did however say that one of his ex british gas colleagues who is now a self employed installer rates them highly and says they are good quality.
id still recommend a vaillant, or the worcester bosch greenstar (depending on how easy you can get spares in belgium)