New boiler Viessmann

[Pulp]

Hi,

I'm thinking about replacing my old boiler - its an ideal Mexico with a cylinder which is about 20yrs old. I have only been in the house for 6 months and the water cylinder is not something we are used to coming from a house with a combi as there never seems to be hot water when we need it. Also the radiators never seem to get very hot as they did in the old house.

I've had someone round on recommendation and he has suggested a Viessmann 100 35kw boiler.

I live in a 4 bed detached house with one bathroom and one ensuite - both currently have electric showers, but the on in the bathroom will be replaced when we refit the bathroom with a boiler heated shower.

The house has 14 radiators - soon to be 15.

Is this a good solution, or should i seek a second opinion? Thanks

 

[JohnD]

when you run the kitchen cold tap into a bucket, and time it, how many litres per minute do you get? If you have a garden tap, try that too.

remember that if you change to a combi, the total flow from all taps/showers/wcs/appliances will be limited by what comes in from the main. If you know what colour and size your incoming water pipe is, that will give some clues. As you have a bathroom and a shower, you may need more water flow.

As for lack of hot water, a well-insulated cylinder will easily keep water hot for 24 hours (or until you use it). Change the hw timer settings so the cylinder is heated for longer, and before/during the times when you are likely to want baths or showers. What size and colour is the cylinder, and can you see how thick the insulation is? Older cylinders are less efficient and slower to heat. A photo will help.

When you get a new boiler, it will be very important to have the old pipes and radiators powerflushed first, and preferably have a system filter fitted, as there is very likely a lot of old sediment in your old system.

Viessmann is a good brand of boiler. Have a look at their website and see if your installer is on their approved list. If so, you will probably get a longer warranty. The website will explain.

 

[Pulp]

Thanks John, the cylinder is at least as old as the boiler. The problem we find is that if the kids have a bath the water is still hot from the morning, but then the tank refills cooling the remaining water in it, then if you want any more water that evening the water is cool or cold, so we have to put the heater back on, but then we might only want to do the washing up, so we effectively heat a whole cylinder of water up to do the washing up, so our thinking is just to get a combi that heats the water when you want it, rather than an system that heats a tank morning and evening that we may or may not use - just seems a waste.

When we had both showers going at the same time, both were just coming off the mains I guess, as they are triton, we did notice they were not as powerful as when using one on it's own, but there was little in it in my opinion.

There are only 4 of us in the house, there is never usually more than one shower on the go at one time and I think on the odd occasion there is we could cope. We are adding another toilet - as the only one downstairs at the moment is outside, but there are three upstairs - one bedroom has a toilet/basin room (mini ensuite) but no shower.

I will try the outside tap tomorrow to see how fast it fills a bucket.

 

[Madrab]

If the hot water cylinder is over 20 years old then the recovery time will pretty long I would think. That means a long time to come back up to temperature, increased energy consumption. A new cylinder with fast recovery time's could be used and be much more efficient and pay for itself over time.

If you don't get hot water when you need it then then system timer/programmer may need to be adjusted so hot water is cycled up to 60deg once or twice a day before you may need it, say early in the morn and in early afternoon.

A combi is really good at delivering one high capacity hot outlet at a time without a drop in delivery, I.e. running the shower and someone turns on the kitchen tap there usually will be a drop in performance. If you're used to that and use it accordingly then fair enough.

A well planned hot water cylinder setup though can usually perform equally to multiple outlets if that's what's required.

You could also keep the cylinder setup with a combi and say run the kitchen hot from the combi for your dishes at night and the Bath/Showers/bathrooms from a new fast recovery HW cylinder removing the costs of running electric showers.

Lots of different plans you could incorporate, depending on your needs. A good plumber would recommend the best plan/option to suit your requirements

 

[JohnD]

if the cylinder is properly insulated, the cost of keeping it hot all day will not be great, so you may as well leave the HW timer on all day.

What size and colour is your hot water cylinder? Can you see how thick the insulation is?

 

[Pulp]

Hi, not very technical this, but the insulation looks like a body warmer and is about an inch thick. The cylinder beneath that looks a copper colour, but not corroded in any way. It's just a metallic copper colour.

No detail on it I can get to, but its about 3ft tall and 18 inches in diameter I would guess.

 

[JohnD]

OK, probably a 36" x 18". they come in a variety of heights and widths.

For a quick fix:

If there is room, you can put an additional red jacket over the top of the old one, the better insulated it is, the longer it will stay hot. Also insulate the pipes around it, especially the one coming out of the top, and the pipes between the boiler and the cylinder. The pipes are probably 22mm diameter.
http://www.wickes.co.uk/search?text=cylinder+jacket

If you have the timer set to HW before, during and after running a bath, it will be fully hot before you start, and reheating even as you fill the first one. Then you will have enough hot water to wash up, and the heat will not be wasted as it will still be hot the next day, but you will benefit from having the boiler on so the cylinder is fully heated before your next bath. A child's bath may take more hot water than an adult's, as a portly adult fills up more of the bath's capacity, so there is less room for water.

The cold water coming in will not (should not) dilute the hot water already in the cylinder, it will lie at the bottom of the cylinder, and the hot water will rise to the top, where it is drawn off from the central pipe and goes to your taps. I went from a 36" high to a 42" high cylinder, and it gives a more generous bath before running out, but the bigger the better. At this time of year the incoming water, and the cold tap, are colder, so it is harder to mix a hot bath.

Longer term,
That old type of cylinder might take about 100 minutes to heat up, it will hold about enough for one bath if it is heated by the boiler. If you were to change it for a modern cylinder, it would be ready-insulated, and depending on your boiler, would heat from cold within about half an hour.

p.s.
have you timed the bucket yet? it's important if you are contemplating a combi.

 

[Pulp]

Hi,

Sorry for taking so long in replying, I've done the bucket test, used the outside tap and filled a 'builders bucket' - 99p wickes type bucket in 31 seconds, then indoors in the kitchen it took 55 seconds, but I think this is more down to the poor quality taps, this type of thing:


http://www.screwfix.com/p/swirl-11473-contract-sink-mounted-deck-sink-mixer-kitchen-tap-chrome/11473

Incidentally I've just had my meter read, only since 29th August to 22nd January I have used 11311kwh of gas - and I only use gas for central heating, no cooker or gas fire. Seems a lot to me, so I think getting the boiler replaced will pay for itself over time.

 

[muggles]

That's 77kW / day. Given that you've got 14 radiators that's probably a load of around 20kW/hr which equates to your heating being on full for 3.5 hours per day. Probably not too far off what you should expect

 

[JohnD]

I've done the bucket test, used the outside tap and filled a 'builders bucket' - 99p wickes type bucket in 31 seconds,

I don't know how big your bucket is, so I can't calculate how many litres per minute that is.

 

[Pulp]

Same as this 14L

http://www.wickes.co.uk/Wickes-Durable-Plastic-Bucket-14L/p/543007

 

[Pulp]

That's 77kW / day. Given that you've got 14 radiators that's probably a load of around 20kW/hr which equates to your heating being on full for 3.5 hours per day. Probably not too far off what you should expect

But given that we didn;t really put it on until November - it seems a lot. Any ideas how much gas 4 hours a day on the Viessman would use?

 

[JohnD]

I went from an old iron boiler to a (not combi) Viessmann, and my gas usage, averaged over several years for each boiler, dropped by about 30%. However this included a programmable room stat, and new TRVs to replace old faulty ones.

Summer usage dropped by about half (combis are less efficient for summer HW as they have to briefly fire up each time you run a hot tap).

The gas savings alone do not cover the cost of change, for the best £ benefit you may as well wait until the old boiler goes badly wrong.

You appear to have about 28 litres per minute coming in, so you could go for an unvented cylinder, which would give you unsurpassed hot water.

I estimate that you have used 1023 cubic metres of gas since November.

I've used 440 cu m since 20th Nov, but it depends how warm the two houses are kept, how many hours a day, how big, or how well insulated they are, or whether you are in the sunny south or the frozen north.

Insulation has a much better payback than a new boiler; so do improved controls. CWI made a big saving, but I no longer have the old usage records from before that.

 

[Pulp]

Thanks, so I'm not doing something stupid?

In terms of the heating use, I work from home 1 day per week, do heating has been on, on occassions, all day, also tends to be on more at weekend, more like 8 hours per day, but apart form that an hour in the mornign and 3 hours in the evening.

For example today my ourdoor thermometer is reading 4c and I don;t have the heating on. So I am thinking I am wasting a lot of gas on the old system.

Also I see Viessman have a weather sensor control that can be added, do these things actually give the claimed 15% saving?

I guess I could add something different in year to come for hot water as solar thermal becomes more cost effective, in 10 years time I'm guessing it will be about a third cheaper for a system and with a south facing roof it's worth considering in 10 years or so.

 

[JohnD]

I don't believe that solar HW is worth the bother. In summer I use half a cu. m of gas per day. My July gas bill was £6.40 for gas and £6.82 standing charge. If solar cut half my summer gas usage, I wouldn't notice it.