Boiler & Immersion vs Combi?

cajef

jennifernil wrote: »

The problem is that the HW should be able to be on without the CH being on, after all......what about summer?

One assumes there is a programmer whereby hot water and heating can be controlled independently, as the OP stated:-

'Both heating and hot water are controlled via a single timer, near the immersion'.

jennifernil

Yes, but they seem to imply that if the heating is off so is the hot water.

i.e, only one time setting is available.

So either it is an odd system, or they do not understand how it works.

EliteHeat

jennifernil wrote: »

or they do not understand how it works.

No, and they are not exactly going out of their way to get any help by providing some relevant information are they?

cajef

jennifernil wrote: »

So either it is an odd system, or they do not understand how it works.

Judging by the OP's original post, I think that the latter may just about hit the nail on the head.:D

mee_2

This might be true, but to clarify:

Firstly, the house is over 70 years old, and has not been modernised, so the system is very old.

There is a large tank in an airing cupboard in the bathroom. This tank is connected to a single timer, which has two switches underneath it. One switch is for heating, the other for hot water. Each switch has 3 options: On, off or timed.

When you run a bath, you can hear the tank re-filling, so I assume this is some form of immersion heater.

In addition, in the kitchen, there is a boiler. When the heating comes on, the boiler begins making more noise, and the flame from the pilot light gets bigger.

But to get back to my original question, which is this: Why pay the cost of electricity to run an immersion heater, rather than using a combi boiler which only heats the water you actually use?

-- Mike

HelzBelz

combi boiler are a fairly recent thing, your immersion heater for the water will probably only kick in if you have the water switch turned to on when the boiler isn't "on" for heating, it won't be what heats your water all the time, the noise in your Hot water tank will just it refilling, not necessarily heating it unless the boiler is on.

Hope this makes sense, I know what I'm trying to say but it might not be typing our correctly

andrew-b

Sorry but i think your still totally missing the point .

Forget combi boilers and what you had previously. First of all you need to understand the basics of how your existing system works. Once we can get past that then we can make suggestions of anything that may be required to improve your existing system.

I believe you have an open-vented gravity system with conventional boiler. In simplistic terms what happens in such a system is that water passes through the boiler where it is heated and then pushed through the pipework by a pump, after the pump there would be what is known as a 3-port motorised valve (probably in your airing cupboard along with the pump).

The 3-port motorised valve can be controlled by the electrical parts of the system to either feed the heated water to the pipework feeding the radiators, or (read this bit carefully!) to feed the heated water to a coiled pipe inside a copper cylinder in your airing cupboard. The coil in the cylinder then indirectly heats cold water (fed from a tank above in the loft usually) outside it within the rest of the cylinder ...where it is then stored for providing hot water to your taps. Note that the water heated by the boiler is not the hot water that comes from the taps.

That is why we asked are there 4 pipes entering the cylinder (2 for heated water to flow in from the boiler and to return back to the boiler to be reheated, and 2 for water coming from a tank in the loft and exiting to feed your hot taps).

The 3-port valve can also be controlled to send heated water to both radiators and cylinder coil at the same time.

The electrical parts of the system would consist of a programmer/timer that controls the times during the day at which the hot water and radiator parts of the system are on or off.

If the programmer says "this is the time to heat hot water" then it consults with a thermostat attached to the wall of the copper cylinder..if the thermostat says "i'm not hot enough" then it triggers the motorised valve to open to feed heated water from boiler to the coil in the cylinder, turn the pump on and ignites the boiler. Once the thermostat on the cylinders say "I'm hot enough now thanks" then it stops the boiler and turns off the pump and shuts the 3-port valve.

If the programmer says "this is the time to warm the house up" then it consults with a room thermostat to see what the current room temperature..if the thermostat says "house is not hot enough" then it triggers the motorised valve to open to feed heated water from boiler to the radiators, turns the pump on and ignites the boiler. Again when the thermostat says "the house is hot enough" the boiler stops and the pump and 3-port valve are closed off.

So where does the immersion heater come into it i hear you cry? Well an immersion heater is a long heating element (exactly the same as in an electric kettle but on a bigger scale) immersed (hence the name) into the water inside the copper cylinder to heat it - instead of being heated by the coil inside fed by heated water from the boiler. Compared to heating the cylinder of hot water via the coil fed by the boiler, an immersion heater is relatively expensive to run. So you would only really use the immersion heater in situations where the boiler was broken.

So what you need to find out is how your system compares to my simplistic description. You need to locate the pump and 3-port motorised valve and see how many pipes are going in/out of the cylinder in the airing cupboard. If you still can't understand it, then either get someone round who is familiar with how heating systems work or post up some pictures on the forum here of inside your airing cupboard and the boiler for us to comment on.

If it were possible, you could have saved alot of hassle by asking the previous owner to tell you how to work the heating before you moved in.

Hope that helps

Andy

jennifernil

Excellent explanation Andrew!

The only thing I would add is that, as this is probably an old time clock, the OP will not be able to choose different times for CH and HW, so unless he leaves the HW switch always at "ON", he will get no more water heated after the time set on the clock, which is also when the CH will go off.

Fitting a more modern time clock with the ability to programme each function independantly should solve his problem. Although he might need additional wiring depending on what is there already.

jennifernil

mee wrote: »

But to get back to my original question, which is this: Why pay the cost of electricity to run an immersion heater, rather than using a combi boiler which only heats the water you actually use?

-- Mike

As Andrew explained those of us without combi boilers are not normally using electricity to heat our water, the electric immersion heater is only there as a back-up.

With a combi, there is no back-up, if your boiler is defunct you have no hot water................which is the main reason I would never entertain having one.

andrew-b

jennifernil wrote: »

Excellent explanation Andrew!

The only thing I would add is that, as this is probably an old time clock, the OP will not be able to choose different times for CH and HW, so unless he leaves the HW switch always at "ON", he will get no more water heated after the time set on the clock, which is also when the CH will go off.

Fitting a more modern time clock with the ability to programme each function independantly should solve his problem. Although he might need additional wiring depending on what is there already.

In our house both the CH and HW programmes are both set for the same times anyway which suits us ok (few hours in the morning and few in the evening - sometimes i'll give it an extra hour boost in the middle of the day if it's particularly chilly or on the rare occassions we run out of hot water )...but yes modern programmers give you more options and let you set different times for different days and differently for CH and HW.

As you say it may just be a case of getting the electrical controls updated.

From a safety point of view, i would also strongly advise when moving into a new property to get the boiler serviced ASAP. I say this from personal experience of having an old boiler with leaky flue and potential to kill us with carbon monoxide poisoning !

Andy