Help: Boiler timer set-up for boiler, tank & cylinder

[larrens]

I have a hot water system that is quite old (15 years or more apparently) & seems to be costing me a lot of money in gas bills. I am not exactly sure how it works or links together.

I would be grateful if someone could guide me in making the most cost efficient use possible of this system from a hot water point of view. I am not worried about central heating at this stage.

I live in rented accommodation, so whilst the boiler is old & inefficient, its not up to me to update it, so at the moment I simply need to live it.

I in my previous house, I had a combi-boiler that provided hot water on demand.

My current house does not have on demand hot water.
I have a boiler, connected to an electronic timer. There is a water tank in the loft & a hot water cylinder in un upstairs cupboard. (I believe this has an immersion heater but it is currently off)

I need to have hot water in the morning, between 6:30am & 9am. My wife & I are at work during the day. We then need hot water again when we get home from work, around 6pm - 11pm.

Currently, the boiler timer is set to go on at 5am & only turn off at 23:30pm, so its on all day covering the hours above which is when I need it. I realise its not actually heating the water continuously, as it gets stored in the hot water tank.

My questions are:
1) should I leave the time as is
2) should I set the timer for the morning & then again at night & if so, how long before I need the hot water must the boiler go on. Similarly, can I turn the boiler off before 23:30 if hot water is being heated & stored earlier on for the bath at 23:00? Someone once said this is not the best option because during the day the water in the tank will cool & use a lot more gas to start heating so much more up again in the evening

Thanks

 

[WHPES]

Does the cylinder have a good thick layer of insulation or a jacket on it?

You could turn the boiler off at say 9pm and there will be plenty of hot water.

 

[larrens]

Thanks - yes, it has a jacket on it

 

[street elbow]

Hi larrens,

To help with your timer problem need more info,

1, is the system gravity or fully pumped? (ignoring gas pipe how many pipes are connected to boiler)

2, how many in the household?

3, do you all bath or shower?

4, do you bath / shower in morning or evening or late night?

5, do you wash up dishes by hand or dishwasher, morning or evening?

6, do you use the hot water for any other purpose?

7, I assume you use your washing machine once a week, when your there.

The reason for all the personal questions, if its a fully pumped system you live alone, only have a quick wash in morning, rinse a coffee mug the system only need be on for 1/2 hr in morning turning off as you get up.

If you are a household of M, D & 2.4 all wanting a bath in the morning with a gravity system 1/2 hr will not heat the water for the first bath, and the mug will get a cold rinse as well.

David

 

[larrens]

Thanks for the reply

1, is the system gravity or fully pumped? (ignoring gas pipe how many pipes are connected to boiler)
I am not sure, how would I find out - I assume pumped as the boiler is low down (in a room slightly lower than floor level) & the water tank is in the loft & water cylinder on the top floor. The boiler is a Potterton Kingfisher II
(I think there are 4 pipes excl gas coming out the boiler - 3 thick, one thin - but I need to double check this)

2, how many in the household?
2 adults, 1 toddler

3, do you all bath or shower?
we all bath - toddler at 7pm, adults around 11pm

4, do you bath / shower in morning or evening or late night?
toddler at 7pm, adults around 11pm. There is an occasional shower at 7am once or twice a week

5, do you wash up dishes by hand or dishwasher, morning or evening?
dishwasher - usually put it on when we go to bed (midnight)

6, do you use the hot water for any other purpose?
no

7, I assume you use your washing machine once a week, when your there.
twice a week, when we are home but there is only a cold water feed into the washing machine

 

[street elbow]

Hi larrens,

If we assume it is a fully pumped system with a standard 36" * 18" DHW cylinder, I would suggest the following:

another way to tell if your system is gravity or fully pumped is to see if there is a thermastat straped to the side of the DHW cylinder. if there is it will be fully pumped, set the stat for 60 degrees

Morning, very little water used so other than the shower so I would put it on for 1 1/2 hours so it switches off as you get up, this will give you a tank full of hot water enough for two showers and odds and ends.

Evening, I would switch it on at about 6.00 to give you enough water for toddlers bath, then leave it on all evening till 11pm so there is enough water for two baths and odds and ends during the evening,

Dish washer and washmac. not a problem as both cold fill only.

David.

If you have a gravity system, you will need to put the timer on for an extra 1/2 to 3/4 hour to give you the same amount of hot water.


If you find you are always running out of hot water then you will need to extend the times, if you some times run out of hot water you can allways press the extra hour button or switch it to constant for an hour (do not forget to swith it back to timed)

I hope this has been helpfull and it reduces the gas bill.

 

[larrens]

thanks for all the advice

 

[larrens]

Last question & excuse my ignorance, if the hot water stays off the whole night & the water in the cylinder cools down, what happens in the morning when the water is heated up & fed into the hot water tank.
Does the hot water not then mix with the cold water already in the cylinder to make a warm mix, or does the cold water get pushed out & replaced with the hot water?

 

[PlumbBobBob]

the water in the hot water cylinder stays in there until drawn off at the taps. it doesn't get topped up by hot water from the boiler, it gets topped up from the cold water storage tank in the loft. it gets heated by hot water from the boiler through the coil in the cylinder. the same water would be used to heat the ch when needed. there is a three way or two two way valves in the system near the cylinder to control where the water from the boiler goes. when hot water only is required the valve(s) activate to direct the water from the boiler through the coil and back to the boiler heating the water in the cylinder. you can have hot water on ch off or hot water off ch on or hw on ch on. bit long winded i know hope it is understandable.

steve

 

[larrens]

understood. Thanks

 

[street elbow]

larrens

A quick lesson on how a heating system works:

To keep things simple, your hot water cylinder has a coil of pipe inside it which heats the hot water,

Think of the coil as a radiator inside the cylinder, when the boiler fires up it heats the water in the "radiator" which then heats the domestic hot water in the cylinder, The water in the hot water cylinder does not go through the boiler it is soly heated by the "radiator"

Another way to look at is like an electric kettle, the element in the bottom of the kettle being like the "radiator" heating the water. only with a DHW cylinder it is designed so it does not boil,

So as the water in the cylinder heats up in much the same way as a kettle its the same water just getting hotter untill you open a tap and use some of the hot water this is replaced by cold water from the tank in the loft and this mixes with the hot water in the cylinder, much the same as re-filling a kettle after making the tea while the water left in the kettle is still hot. Then the water is heated again untill it reaches the desired temperature.

When you use hot water and the cold water replaces what you have used the cold water stays at the bottom od the cylinder and the hot water rises to the top of the cylinder (heat always rises) the outlet of the hot water cylinder is at the top so you will always draw of the hottest water in the cylinder.

If you run your hand over the cylinder you will find it is very hot at the top getting cooler as you move down and it will feel cold at the bottom

The systems are designed so that the cylinder is always full of water.

Hope this helps

David.