More efficient central heating

M

mseymour

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• 15 Oct 2010

• #1

We have a tank system which is gravity fed and the boiler provides both hot and cold water.

The boiler is around 20 year old with a balanced flue. When we had it fixed recently the engineer said that it was a hot water priority boiler. We'd rather not replace the boiler although we know it is very inefficient as there is so little to go wrong with these older boilers.

We need to have the central heating on more often, but the problem is that controls only allow us to have the central heating on with the hot water as well. This means that if we need a bit more heat in the middle of the day or night we cannot do that without also heating up a tank of water as well. I know that this is very inefficent, but our controls don't allow us to do anything else.

Is this restriction of having central heating with hot water likely to be a constraint caused by the controls or the boiler type? How hard is it to fix a new control unit? I can do most DIY electrical jobs and understand electronics.

Thanks for your help.

 

C

compheat

• 15 Oct 2010

• #2

To have your heating on and hot water off you need to install a valve, this can either be a motorised valve controlled by a thermostat or a manually operated valve that you turn off your self.

When your cylinder gets to the same temp as the heating pipe work it wont get any hotter, make sure your cylinder is well lagged.

 

A

ajrobb

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• 15 Oct 2010

• #3

It sounds like there might be a motorised valve that directs boiler output either to the hot water cylinder or to the central heating. Modern timers can allow hot water and central heating to be on at different times (e.g. have the water heating an hour or so before the central heating comes on in the morning). That way, the hot water normally won't delay the central heating coming on.

Of course, it could be a really old system with a gravity feed to the cylinder and a thermostat on the return from the cylinder that delays the pump coming on.

 

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mseymour

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• 17 Oct 2010

• #4

Hi, Thanks for your comments. I've had a look around the hot water tank and there does appear to me a motorised value that is called a value actuator pump.

There is pipework coming up from the floor that leads into this and there are two pipes leading from it. One to the hot water tank and the other going up to another pump into the ceiling.

Could that motorised value be what I need to install this sort of control?

The other thing I should have mentioned is that it is possible to have the hot water on without the central heating, but the set of controls does not allow central heating without hot water.

I'm wondering if this is a limitation of the controls or is it ever the case that there is a system will allow hot water without central heating but not central heating without hot water?

Thanks for your help.

MS

 

vulcancontinental

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• 17 Oct 2010

• #5

It sounds as though you have a gravity hot water, pumped central heating system which could be converted to what you want but a picture would help.
It's not the principle of conversion it's also the space available in the airing cupboard and on available pipework to install what you need. A Honeywell C plan is what I would guess at but as for keeping the old boiler - yes, for fewer problems but higher energy costs - spot on.

 

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mseymour

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• 17 Oct 2010

• #6

Hi,

Thanks for your comments, do these pictures help or do you need more detail?

Let me know if you need more.

thanks,

MS

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• mseymour
• 17 Oct 2010
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petit_pablo

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• 17 Oct 2010

• #7

Looking at the pictures i would imagine you dont have a HW off from the cylinder stat to the mid position valve grey wire and likewise, no Hw off from the timer to grey wire.
Can you check this?

Also what type of timer is it?

 

vulcancontinental

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• 17 Oct 2010

• #8

I'd check the timer first. A picture? Many have a small dipswitch or screw inside that will permit what you want as the control system already comprises the components necessary.

 

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mseymour

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• 17 Oct 2010

• #9

Here is a photo of the timer. Just to clarify what happens. I can slide the bottom slider across to have just the hot water on, but I cannot slide the top slider (central heating) without it also moving the bottom one and turning on the hot water as well. There is something inside the control that is linking the two, could this be the sort of thing that might be removable?

Thanks for your ideas petit_pablo. I don't really know exactly what I need to check? Do you need to test the wiring? Is there a way of checking this by the heat on the pipes going to or from the boiler when the system is on?

Thank you very much for the help. It is really appreciated.

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vulcancontinental

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• 18 Oct 2010

• #10

Yes there is a locking pin.

It may be the answer and it's the first thing to check. Turn power to the system off. Loosen the two small screws on the underside of the timer and lift off (bottom edge swings outwards then up). on the back of the unit you'll see a slotted piece of nylon; turn it a quarter turn so the slot in the nylon is parallel with the length of the channel it is in. The nylon piece should move freely then.

If your wiring is correct you should be able to do what you want except choose different times for heating and hot water (the same times govern both channels) on this timer.

i.e. you could set heating for once a day but hot water an hour morning and afternoon or simply turn water off but keep heating on.

It is a standard backplate and if you buy a digital programmer that utilises the same backplate it would give you different times for heating and hot water three times a day without changing the wiring.

All this depends on the existing wiring being correct. As petit says, you need three wires from the cylinder stat to the wiring centre. Check the timer first then try the system out.

 

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mseymour

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• 20 Oct 2010

• #11

Hi, I've worked all these out now. In the end we called out British Gas because it was not working as it should have been. Not just a case of needing it to be more effective for us, we were finding that we had either heating or water, but not both.

The solution was:

1) Replace the motorised value. It turns out that it had been fitted (by the previous British Gas man!) with a two way motorised value as opposed to a three way valve so we either had the water going to heat the cylinder or the central heating and then there was a bit left for the central heating from the cylinder, but not much. That was why the radiators did not work well.

2) When the engineer replaced that part he tried moving the pin on the back of the control which allowed separate movement, but it did not work. When he tried to put the pin back it broke and he ended up replacing the timer with a new unit.

So it is all working very well now which is good news as the temperate has really just started to drop significantly overnight!

Thanks for your help. I really appreciate it.

MS