New Viessmann boiler

Hello

My Boiler, a Glow warm Ultimate 40 FF/LP has broken this week with various new parts required so have decided to get a new boiler.

I have been recommended the Viessmann Vitodens 100-W High Efficiency Combination Boiler, with weather comp controls (at additional cost), we are on LPG so any saving is worth considering.

I have been through the forums and read mixed reviews for this boiler. It will come with a 5yr warrantee as the fitter has taken the course and he has experience fitting them.

Currently our hot water is heated through an immersion tank overnight using eco7. It is electric only so we would take that out and gain some extra storage space.

We have one kitchen and one bathroom with an electric shower but I am hoping to install a manual mixer shower from the boiler. There are 8 radiators. The house is a terraced edwardian cottage built in 1840 and loses heat fairly quickly even though there is double gazing throughout. I think the smallest 26kW model will be suitable but I have been unable to get the energy savings trust boiler sizing calculator to work. Is anyone able to advise on boiler sizing?

The fitter is quoting me for a 26kW and 30kW and has just said that the bigger it is, the better the flow rate but I have read that the bigger ones might be less efficient with my requirements for CH.

Does anyone have experience with the flow rate from the smaller 26kW model for showers?

Are the weather comp. controls worth it as we do not have a north facing wall to put it on? It could go on the south facing but then it will get hit by the sun

Thanks for your help
David

You need to get the installer to measure the flow rate you have, and size the boiler accordingly. Either model will be more than enough for your heating requirements. Combis are sized for hot water demand.

The vitodens is a very good product. The 100 is a new product, and any of the earlier problems have been ironed out.

sloons said:

I have been unable to get the energy savings trust boiler sizing calculator to work. Is anyone able to advise on boiler sizing?

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I am having problems with the EST calculator as well. Are you using Firefox or Internet Explorer?

Try the Sedbuk Boiler Calculator. It will give the same answer as EST, but is not so user friendly. Don't forget that these calculators are not designed for combi boilers; they assume a hot water cylinder. If you deduct 2kW from the final result you will get your heating requirement. When choosing the combi boiler, make sure that the heating output is sufficient and that it will modulate below the calculated heating requirement. The lower it goes the better.

The fitter is quoting me for a 26kW and 30kW and has just said that the bigger it is, the better the flow rate but I have read that the bigger ones might be less efficient with my requirements for CH.

Does anyone have experience with the flow rate from the smaller 26kW model for showers?

Click to expand...

The size of boiler is determined by the mains flow rate and pressure.

Are the weather comp. controls worth it as we do not have a north facing wall to put it on? It could go on the south facing but then it will get hit by the sun

Click to expand...

Does your house have only one external wall? Which direction does each external wall face? South is definitely no good.

Thanks for your reply

D_Hailsham said:

I am having problems with the EST calculator as well. Are you using Firefox or Internet Explorer?

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Firefox on the mac but i have just tried safari and it is working fine now, never thought to try a different browser.

Does your house have only one external wall? Which direction does each external wall face? South is definitely no good.

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Haha East and West facing but all the rooms we occupy have windows facing west so I suppose it could go on the west side but is still going to get sun.

sloons said:

Firefox on the mac but i have just tried safari and it is working fine now, never thought to try a different browser.

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Off topic, I know - but that's interesting. I can't get it to run in Windows Firefox either. I emailed EST and they said there was nothing wrong; they can get it to run in FF. The fault I got was that you would fill in the dimensions and no of floors and press Next. The screen would refresh and thn the same screen would appear, with the boxes empty. Did you have the same problem?

Back to your problem ...

East and West facing but all the rooms we occupy have windows facing west so I suppose it could go on the west side but is still going to get sun.

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A mid-terrace cottage then. If you go for a weather compensator, install the sensor at the north end of the west wall. It will then not get any sun until toward the end of the day.

D_Hailsham said:

Off topic, I know - but that's interesting. I can't get it to run in Windows Firefox either. I emailed EST and they said there was nothing wrong; they can get it to run in FF. The fault I got was that you would fill in the dimensions and no of floors and press Next. The screen would refresh and thn the same screen would appear, with the boxes empty. Did you have the same problem?

Click to expand...

Exactly the same. I think the EST might have an old version of FF or not tried it at all...

A mid-terrace cottage then. If you go for a weather compensator, install the sensor at the north end of the west wall. It will then not get any sun until toward the end of the day.

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You think it worth going for it the weather comp then? I am quite happy with my existing wireless thermostat but if the weather comp will make the boiler more efficient

I am thinking of replacing all my radiators as the fitter has recommended a powerflush which would cost the same! I have been running the system with no inhibitor for a year and the house was drained down for a year before that. I'm worried the radiators will have corrosion - due to my lack of care and knowledge. From what I have read, that may reduce the efficiency and life of the boiler. What do think? Is it worth replacing them all and giving the CH a fresh start? Some radiators frequently filled up with air previously (from the top) however that may be due to the faulty expansion tank on my old boiler letting air in the system

sloons said:

You think it worth going for it the weather comp then? I am quite happy with my existing wireless thermostat but if the weather comp will make the boiler more efficient

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Which wireless stat do you have?

I am thinking of replacing all my radiators as the fitter has recommended a powerflush which would cost the same!

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But that would not remove any sludge lying in the pipes.

I have been running the system with no inhibitor for a year and the house was drained down for a year before that. I'm worried the radiators will have corrosion - due to my lack of care and knowledge.

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Tut, Tut.

From what I have read, that may reduce the efficiency and life of the boiler. What do think? Is it worth replacing them all and giving the CH a fresh start? Some radiators frequently filled up with air previously (from the top) however that may be due to the faulty expansion tank on my old boiler letting air in the system

Click to expand...

A lack of inhibitor will mean corrosion and consequently sludge in the system, which can block up the heat exchanger, pipes and radiators. Even if you replace all the rads, you will need the pipes flushed to make sure they are clean. It would be sensible to have a sludge filter fitted, e.g. Magnaclean, Spirovent etc.

If you do replace your radiators, you can then make sure they are sized to take advantage of the weather compensator. This usually means installing rads which are 15-20% larger. The reason for this is that they will give of less heat due to the wider temperature differential used on condensing boilers.

What size boiler did the online calculator give? Deduct 2kw from the result then increase the answer by 20%. This will be the total nominal (manufacturers quoted) radiator output you require.

All calculators assume an outside temperature of -1C. You may think it worth allowing for lower temperatures. . The calculation is simple.

If heat for -1C, 21C is 11kW, the heat for -5C, 21C is 11 x ((21-(-5)) / ((21-(-1)) = 11 x 26 / 22 = 13kW

This will affect boiler and radiator. As you are installing a combi you will probably find that the CH output is more than adequate, so you only have to upsize the rads to allow for a lower outside temperature and their reduced output.

KevC1 said:

You need to get the installer to measure the flow rate you have, and size the boiler accordingly. Either model will be more than enough for your heating requirements. Combis are sized for hot water demand.

The vitodens is a very good product. The 100 is a new product, and any of the earlier problems have been ironed out.

Click to expand...

we will see in five years and not before!!! still a white elephant tho.

D_Hailsham said:

Which wireless stat do you have?

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Its a Horstmann HRFS1

A lack of inhibitor will mean corrosion and consequently sludge in the system, which can block up the heat exchanger, pipes and radiators. Even if you replace all the rads, you will need the pipes flushed to make sure they are clean. It would be sensible to have a sludge filter fitted, e.g. Magnaclean, Spirovent etc.

Click to expand...

Will it be ok to run the system on a sludge filter and then replace the radiators if there are any problems?

If you do replace your radiators, you can then make sure they are sized to take advantage of the weather compensator. This usually means installing rads which are 15-20% larger. The reason for this is that they will give of less heat due to the wider temperature differential used on condensing boilers.

Click to expand...

Ok so does this mean it is better if cooler water is returning the boiler? My radiators at the moment total 8kW does this mean the boiler would not run efficiently?

What size boiler did the online calculator give? Deduct 2kw from the result then increase the answer by 20%. This will be the total nominal (manufacturers quoted) radiator output you require.

Click to expand...

The est calculator gave 30kW boiler so this means I need 33.6kW in radiators. I would have no room for furniture

sloons said:

Its a Horstmann HRFS1

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That's a real oldie! I would ditch it. Weather comp will give you much better control.

Will it be ok to run the system on a sludge filter and then replace the radiators if there are any problems?

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Yes, but the system will still need flushing when the new boiler is installed. Find out how long the installer thinks a power flush will take; with eight radiators it should be at least two hours.

Ok so does this mean it is better if cooler water is returning the boiler?

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Yes. Boilers only condense when the return temperature is below 55C.

My radiators at the moment total 8kW does this mean the boiler would not run efficiently? Also remember to press the Calculate button on each page.

The est calculator gave 30kW boiler

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Something wrong there I think.

Assuming the house is warm enough and you only have 8kW of radiators, you should not need a 30kW boiler. I suggest you run the calculator again. Then, if you get the same result, post the data you have used, so it can be checked. One thing to remember is that on page 2, where it asks for number of external walls, you only have two (length) and 0 (width) as you have a mid-terrace house. Length=frontage, width=depth.

onlyfitidealboilers said:

KevC1 said:

You need to get the installer to measure the flow rate you have, and size the boiler accordingly. Either model will be more than enough for your heating requirements. Combis are sized for hot water demand.

The vitodens is a very good product. The 100 is a new product, and any of the earlier problems have been ironed out.

Click to expand...

we will see in five years and not before!!! still a white elephant tho.

Click to expand...

I can't believe an installer that only fits ideals has the front to comment on another boiler! Viessmann boilers are a good product OP, run a mile from an installer who wants to put an ideal in your home

D_Hailsham said:

Assuming the house is warm enough and you only have 8kW of radiators, you should not need a 30kW boiler. I suggest you run the calculator again. Then, if you get the same result, post the data you have used, so it can be checked. One thing to remember is that on page 2, where it asks for number of external walls, you only have two (length) and 0 (width) as you have a mid-terrace house. Length=frontage, width=depth.

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length - 8
width - 6
height - 7
number of floors - 2

external walls length - 2
external walls width - 0

mid-terrace
double glazed plastic
solid wall

pitch roof <50 mm insul (cannot get access to all areas of roof space)
north midlands

This comes to 27kW, still much higher that my existing radiators.

I used 1 external wall (width) previously to get 30kW as on one side there is an empty garage.

onlyfitidealboilers said:

KevC1 said:

You need to get the installer to measure the flow rate you have, and size the boiler accordingly. Either model will be more than enough for your heating requirements. Combis are sized for hot water demand.

The vitodens is a very good product. The 100 is a new product, and any of the earlier problems have been ironed out.

Click to expand...

we will see in five years and not before!!! still a white elephant tho.

Click to expand...

this has to be a joke? viessmann boilers are superbly engineered and are right at the top of the list when it comes to quality. early 100s did have problems - and the manufacturer was quick to accept that there were issues and they went out and repaired/replaced parts without any quibble. unlike any other manufacturer i have come across.

perhaps i should change my forum name to 'i_repair_ideal_boilers_(frequently)'. and sometimes i scrap them before they have reached their tenth birthday.

onlyfitidealboilers said:

we will see in five years and not before!!! still a white elephant tho.

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That would still be longer than ideals last.

HootingOwl said:

onlyfitidealboilers said:

KevC1 said:

You need to get the installer to measure the flow rate you have, and size the boiler accordingly. Either model will be more than enough for your heating requirements. Combis are sized for hot water demand.

The vitodens is a very good product. The 100 is a new product, and any of the earlier problems have been ironed out.

Click to expand...

we will see in five years and not before!!! still a white elephant tho.

Click to expand...

this has to be a joke? viessmann boilers are superbly engineered and are right at the top of the list when it comes to quality. early 100s did have problems - and the manufacturer was quick to accept that there were issues and they went out and repaired/replaced parts without any quibble. unlike any other manufacturer i have come across.

perhaps i should change my forum name to 'i_repair_ideal_boilers_(frequently)'. and sometimes i scrap them before they have reached their tenth birthday.

Click to expand...

what on earth you complaining about then. pays ya mortgage doesn't it!