Hot water cylinder on Combi boiler

[johno12345]

Hi,

I am considering adding a hot water cylinder to my existing combi boiler. Is there any compelling reason that such a setup would be unfesible. I would cap off the combi hot water supply and use the cylinder instead.

The controls would require 2 zone valves and another timer but other than that, I cant see any problems (that doesnt mean there arent any!)

Thanks

 

[BigBurner]

More info.

Is it unvented?
A tank/cylinder?

Why are you doing this?

 

[johno12345]

vented, tank & cylinder

I want better hot water than can be achieved from a combi boiler

thanks

 

[namsag]

No reason not to and quite straight forward to wire up
Saves buying a new boiler.

 

[johno12345]

glad you agree

I got the combi for budgetary reasons but I miss proper hot water. I am sure some are better but mine, and all the others i have used give either lots of tepid water or small amounts of scalding hot water!

 

[spudkey]

Maybe keep combi hot water outlet to supply just kitchen sink as this tends to get used more througout the day and may result in having to heat cylinder less

 

[johno12345]

I suppose I could, there would only be about 3m of pipework between the cylinder and taps so doesnt really seem worth it

 

[BigBurner]

I would use a combination cylinder to provide hot water - all one neat insulated unit. This may be viewed as an unvented cylinder with an air break. You may want to have a 3/4" ballcock with a 22mm mains pipe to the combination cylinder to fill it sharpish. Have the combi boiler do the showers(s) only. The the rest of the taps from the cylinder. This will ensure less problems, and greater boiler longevity with the combi as the DHW section will switch on and off only a few times a day, not repeatedly as with a kitchen tap. Have a quick recovery coil in the cylinder.

Don't go for a separate tank and cylinder setup.

 

[johno12345]

I was planning to use the cylinder for the shower and other 2 taps.

The water flow is very poor, the supply from the street is only 15mm copper. If I use one cold tap and someone uses another, the flow is reduced quite badly. I was thinking of placing the tank up as high as possible and the cylinder in the loft supported by the internal brick walls

Thanks for the advice so far

 

[DP]

Been there, done it, got the tee shirt.

My own hoose was fitted with a combi running three zones (bedrooms, living rooms and hot water cylinder)

Best option as already pointed out, would be to get the boiler to supply kitchen and utility rooms with hot water. I would opt for an unvented cylinder for remaining HW needs. I would also ensure it was fitted by someone who does it by the book (not just chucked in) and cold feed was a balanced feed (often not done). Also, ensure immersion heater is cabled for use in emergency.

 

[BigBurner]

I would opt for an unvented cylinder for remaining HW needs.

As his cold water mains is abysmal an unvented cylinder is a waste of time. They are waste of time in most cases anyway and ....that annual service charge?

 

[BigBurner]

I was planning to use the cylinder for the shower and other 2 taps.

The water flow is very poor, the supply from the street is only 15mm copper. If I use one cold tap and someone uses another, the flow is reduced quite badly. I was thinking of placing the tank up as high as possible and the cylinder in the loft supported by the internal brick walls

Thanks for the advice so far

With such poor cold mains water pressure. You may want to consider an accumulator - a cold water storage cylinder under pressure from the mains. It charges to the static water pressure. What size is the combi in kW? It may be OK, and the problem is your cold water mains.

Is it possible to upgrade the mains pipe and sort it forever?

In your case I would consider a high flow combi and a cold water accumulator. It will belt out the flow and pressure to all taps.

 

[BigBurner]

I was planning to use the cylinder for the shower and other 2 taps.

The water flow is very poor, the supply from the street is only 15mm copper. If I use one cold tap and someone uses another, the flow is reduced quite badly. I was thinking of placing the tank up as high as possible and the cylinder in the loft supported by the internal brick walls

Thanks for the advice so far

With such poor cold mains water pressure. You may want to consider an accumulator - a cold water storage cylinder under pressure from the mains. It charges to the static water pressure. What size is the combi in kW? It may be OK, and the problem is your cold water mains.

Is it possible to upgrade the mains pipe and sort it forever?

In your case I would consider a high flow combi and a cold water accumulator. It will belt out the flow and pressure to all taps and shower mixers.

What is the pressure of your cold water mains with no taps running?

 

[johno12345]

dont really fancy an accumulator, im trying to keep it simple. I only have 2 taps and a shower. The boiler is 30kW and is only 2 years old.

Not sure of the cold pressure but I can stop it with my thumb quite easily

The mains pipe runs out the back, curves around the garage, to the left a bit then under the drive and connects to the main water pipe under the main road so it would probably be a bit tricky.

 

[BigBurner]

dont really fancy an accumulator, im trying to keep it simple. I only have 2 taps and a shower. The boiler is 30kW and is only 2 years old.

Not sure of the cold pressure but I can stop it with my thumb quite easily

The mains pipe runs out the back, curves around the garage, to the left a bit then under the drive and connects to the main water pipe under the main road so it would probably be a bit tricky.

30kW would be fine for your needs. The problem is the cold water mains supply, not the combi. The water company are supposed to supply 1 bar minimum. Get them out to check it.

If no luck, then fit a plastic cold water tank fed from the mains, having only the kitchen tap from the mains pipe, and fit a pump, pumping from the tank to the cold water taps and combi. You get the best of everything then: pumped showers and high pressure everywhere with enough DHW. This is most likely the cheapest route and most cost effective to get up to speed on this.