Still confused.....central heating upgrade

[VioletG]

Hi,

I posted a while back about a new combi boiler and since then I have had further quotes.

My dilema is to go with a combi boiler or a system boiler with tank in attic etc.

It's a 3 bed semi detached, a living room, dining area, small kitchen and back extension. One bathroom/shower, expanding to two.

Now I know that the system boiler can apparently cope with two bathrooms. But Im concerned about a combi solution.

If for example someone turns on the cold water or flushes the toilet I dont want to be screaming downstairs for someone to turn it off.

Is a combi going to allow for this?

I did ask before but it seemed to delve into various arguments about the best boiler.

On one hand I have been quoted on a Wocster Bosch Greenstar 30 kw CDI, a Glow-worm Ultracom 38cxi and a Vaillant ecoTEC plus 831

In terms of a system boiler - Glow-worm Ultracom 18sxi or a Vaillant 618 System and a 42˝x18˝ indirect, pre-lagged copper cylinder.

Obviously the combi seems great in terms of space etc, but I will happily live with a copper cylinder if it means its not going to mean a shower nightmare.

 

[D_Hailsham]

It's a 3 bed semi detached, a living room, dining area, small kitchen and back extension. One bathroom/shower, expanding to two.

The problem with both combi and sealed cylinders is that both systems supply the hot and cold water direct from the mains. This means that, if the flow rate and water pressure is not high enough, flushing the toilet may be noticed by someone in the shower as a lower flow rate. This will be minimized by installing thermostatic showers.

All combi boilers have built in temperature control to stop the hot water exceeding the set temperature.

On one hand I have been quoted on a Wocster Bosch Greenstar 30 kw CDI, a Glow-worm Ultracom 38cxi and a Vaillant ecoTEC plus 831

In terms of a system boiler - Glow-worm Ultracom 18sxi or a Vaillant 618 System and a 42˝x18˝ indirect, pre-lagged copper cylinder.

As you can see, the real advantage of a sealed HW cylinder is that you can use a much smaller boiler (18kW v 30+ kW) as you are not having to heat the water instantaneously.

Have you checked your cold water flow rate at the kitchen tap? Use a marked bucket and a watch. You need over 20 litre/min for a sealed cylinder.

 

[VioletG]

Thanks, ours i believe is 16ml per minute

My preference would be a combi but my concern mainly is due to my parents home, they have a combi, as part of the warm front scheme.

They have a four bed house and 2 bathrooms. The shower is awful, someone flushes the door stairs loo I have to wait several minutes, sometimes longer for it to return to hot water and a normal flow.

Even if they turn the cold water to fill a kettle, the shower almost comes to a halt.

Coupled with the fact that so many people seem to argue the best combi boiler, that perhaps there isnt one and the old system is the best.

 

[transam]

As general rule of thumb ?? any combi will be less reliable than a heat only /system boiler , a combi always works harder ??

If you have a cylinder you would ?? have an immersion heater which will provide back up if required !!

 

[ajrobb]

The main problem is stored hot water has to be heated above 60°C for over an hour to kill legionella bacteria. Apparently about 60 people a year die from immersion in hot water, mostly the very old and the very young. Stored hot water loses heat but saves water.

The standard set up is to have the same boiler temperature heating both hot water and central heating. However, condensing boilers need a low return temperature to work at maximum efficiency. Some condensing system boilers can have separate temperatures for hot water and central heating and there is even weather compensation on central heating to save about 5% of annual gas consumption.

Most combination boilers don't store hot water so don't have to heat hot water to dangerous temperatures. However, you can wait nearly a minute for hot water in a bathroom basin.

If you like a bath then a cold water tank in the loft and a vented cylinder can often fill a bath quicker than an unvented cylinder and much quicker than a combination boiler. Add a pump and you can have a proper power shower, not limited by your mains water supply. Pumps are noisy, so might not be suitable if you need a shower late at night or early morning.

An unvented cylinder supplies hot water at practically the same rate as your mains supply. This can give a 'good' shower, at least as good as a combination boiler and usually better.

Toilets can be fitted with flow restrictors. They not only make toilets quieter, they reduce the effect on showers.