system boiler hot water issues

[wta99]

I should be grateful if you help me with the following query. I had a Worcester green star 30 CDI system boiler (natural gas) installed a couple of months ago. It is connected to a 210 litre unvented mains pressure water cylinder (indirect?) , together with a three channel seven-day electronic programmer (one channel upstairs heat; one channel downstairs heat; one channel hot water heating). To my disappointment, I note that whenever the central heating is turned on then the stored hot water is drained from the cylinder. I asked my installer/engineer about this and he informed me that I should turn the hot water heating on for about 20 to 30 minutes before I turned the heat on i.e. in order to ensure that the water in the cylinder remained hot. Clearly this is not practicable especially whenever one wishes to push a ‘boost’ of heat. Moreover, it represents a waste of energy to have to run the boiler for an additional period than is necessary for the central heating in order to heat the same water once again before the central heating comes on.

Would you please confirm whether or not it is feasible for the hot water tank to be isolated from the central heating? I.e. so that whenever the central heating is turned on, it does not drain the stored hot water from the cylinder. It is my understanding that such a scenario would be much more economical and efficient. It is clearly ludicrous to sacrifice all the stored hot water every time one turns on heat. I appreciate that there is a device called an optional integral diverter and I would welcome clarification as to whether such a device would address my problem. I look forward to hearing from you and I appreciate your assistance.

 

[simond]

The hot water cylinder should be 'zoned' separately from the central heating by one of three zone valves on your system.

It would be almost impossible to plumb the system so the CH exhausted the heat in the cylinder. NB: Have you tried the system without the CH, and does this give you HW?

I therefore have to conclude you are either confused or your heating technician has done something incredibly silly.

The Worcester optional diverter valve ties you to Worcester proprietary controls and also only works correctly with a single zone of heating, this is not the answer to your apparent problems.


Having read your post again, it is a sensible suggestion to run your HW charging programme before the heating is due to come on. Your installer seems to be on the money.

 

[wta99]

Dear Simon,

Thank you for your reply.

In answer, I respond as follows:

* I ran the system without central heating during the summer and it worked well for hot water.

* why is it necessary to run the hw cycle before running the ch cycle? i.e. if the water is hot is it not a waste of gas to run it again?

* can the hot water cylinder not be isolated in such a way that the ch cycle should not affect it?

Kind regards,

Wayne

 

[simond]

1. That suggests it is all correct
2. The energy created by the gas in terms of heating the boiler water is then transferred to the (colder) water stored in the cylinder. Once the cylinder reaches temp, the boiler is automatically turned off.

The HW cylinder will heat up quicker when there are not other demands on the boiler such as your radiators. The shorter, more powerful burn uses less gas.

On the coldest days of the year, your CH will need more energy from the boiler. In these periods the HW recharge will both take longer and delay the warmup of the rads. So this is the other reason why you might be better separating the timings.

A tepid bath on the coldest day of the year is otherwise likely to result.....

3. By the sound of it, that is what you have. 3 separate zones.
If you want the zones to be totally segregated in terms of performance you would need separate boilers- and that would be silly for a small domestic property.

 

[wta99]

Simon,

Thanks for this. It is very helpful. One query remains. If my hot water cylinder is heated (i.e. water is warm) why does the water temperature diminish if the central heating is turned on? i.e. surely the cylinder should just retain the heat? Or does the central heating water have to pass through the cylinder too?

Wayne

 

[simond]

Can you give the make and model of your unvented?

 

[Agile]

You seem to have some misconceptions about how your system works.

As stated its difficult to imagine any way that the cylinder could be cooled once its been heated. Why do you wrongly think that happens?

You also seem to imagine that gas is used all the time when the time clock is set for water heating. That is NOT the case! Immediately the water is hot the thermostat turns off the heat source.

Tony Glazier

 

[D_Hailsham]

It is connected to a 210 litre unvented mains pressure water cylinder (indirect?) ... To my disappointment, I note that whenever the central heating is turned on then the stored hot water is drained from the cylinder.

I think you may not completely understand how your cylinder works.

When the boiler is ON and the HW zone valve is open, the boiler water circulates through a coil in the cylinder and heats up the water in the cylinder.

If you draw off hot water by opening a tap, the hot water in the cylinder is replaced by cold water direct from the incoming mains. This means the temperature of the water in the cylinder will get colder the more you draw off the hot water. Unless, of course the boiler is ON and the HW zone valve is open.

If the central heating is running a t the same time as the cylinder is being heated, the output of the boiler has to be shared between the CH and the HW. How much is available for the HW will depend on the difference between the boiler output and the CH requirement. Obviously when the CH is not on, all the boiler output is available to heat up the HW.

 

[wta99]

Simon,

It is a CenterStore Solar 210 litre unvented mains pressure water heater (nb presently no solar connection).

Thanks,

Wayne