Central Heating and Hot Water will not work at the same time

[firks]

Hi,

I have a strange problem with my central heating/water system, it has been this way since we moved into our current house.

The problem is that the central heating and hot water cannot be on at the same time. In addition, the only way to get either to come on is to follow this bizarre sequence:

To get central heating on - turn on hot water (either by timer or advance button on control), turn on heating, turn off hot water. Only at the point of turning off hot water will the system then fire into action.

Similarly, to get HW to turn on - turn on CH, turn on HW, turn off CH.

I have had plumbers out for other issues in the past 18 months and they've always said "we don't do electricals, but it looks like it needs re-wiring" which isn't that helpful.

Anyone have any ideas what could be causing this? Is it a wiring problem? A problem with the control? The 3-way valve? Anything else? Should I just find someone who knows what they're doing to come out and fix it for me at an exorbitant cost?

Any suggestions gratefully received.

Thanks
Tim

 

[linkyplumb]

It all depends on the sytsem configuration.
It could only have a 3 way diverter valve, instead of a mid position valve, so there is no way of getting both by just replacing the programmer.
Similarly it could have a mid position valve, and just needs a programmer upgrade.
What controls are there?
Any pics that you could upload?
It may be prudent ot get someone in.... it may not cost as much as you think.
Graham

 

[mysteryman]

Many modern systems are water priority - for good reason. It has been the norm elsewhere for decades.

 

[stem]

The wiring of a system with a 3 port valve is quite complicated and requires a bit of knowledge in order to troubleshoot. Sometimes there may be more than one fault. I have made a simple sketch of the switching part of the wiring below to assist. For clarity, I have omitted the main electrical supply, neutrals and earth connections, as well as the pump wiring because this can vary slightly from system to system.The basic principles are:

1. The white wire to the 3 port valve should be live whenever the heating is “ON” at the programmer and the room thermostat is also “ON” (calling for heat.)

2. The grey wire to the 3 port valve is live whenever the hot water is “OFF” either because it’s off at the programmer or the cylinder thermostat is not calling for heat. (Satisfied)

3. The orange wire to the 3 port valve is live when the central heating only is required (it’s used to switch on the boiler. When the hot water is running, this operates the boiler directly via the cylinder thermostat)

4. When the hot water cylinder thermostat is calling for heat this switches the boiler on directly.

If you are able to check the wiring you have safely, see if it corresponds to the drawing. (You will likely have to trace the connections through terminal boxes or a wiring centre) If the connections are not as shown, please say (or draw if possible) what you do have. It’s not uncommon for someone to do a DIY swap of the cylinder thermostat or programmer and connect one or more of the wires incorrectly. If you are not competent to do these checks, then the troubleshooting is probably outside of your capability and you would be best to call in a professional.

Untitled

• stem
• 11 Jan 2012
• 1

 

[Agile]

Hi,

I have had plumbers out for other issues in the past 18 months and they've always said "we don't do electricals, but it looks like it needs re-wiring" which isn't that helpful.

Anyone have any ideas what could be causing this? Is it a wiring problem? A problem with the control? The 3-way valve? Anything else? Should I just find someone who knows what they're doing to come out and fix it for me at an exorbitant cost?Thanks

Tim

What do you expect if you call plumbers! You need a proper heating engineer who will be fully competent to deal with design or wiring issues.

I am afraid that rather than some cheap itinerant plumber you will need a competent heating engineer. I would charge an £84 diagnostic fee in the local area and in most cases that would cover sorting a simple wiring error if that was the cause.

What do you consider is an exorbitant cost?

Tony

 

[firks]

Thanks all for your replies. A bit more information on what's installed:

The controller is one of these: http://www.plumbworld.co.uk/invensys-lifestyle-111-2319#

The actuator is one of these: http://www.plumbnation.co.uk/site/drayton-ma1-22mm-3-port-mid-position-motorised-valve/

The whole system was installed by the guy who owned the house previously; he is a Corgi engineer but he seems to have cut a lot of corners with a lot of his DIY projects!

Tony, I called plumbers because I had plumbing problems... I just happened to ask them if they knew what the problem was.

Sounds as if I should call someone out as I'm reasonably competent with troubleshooting electrics/wiring but this sounds like it may be complicated, particularly given the poor standard of installation (e.g. makeshift wiring centre)[/url]

 

[acmedone]

Hi,
I have a strange problem with my central heating/water system, it has been this way since we moved into our current house.

After my son moved into his house he noticed a strange problem. For some reason, the heating would not come on. A bit of fiddling with the override buttons on the programmer revealed that there was nothing wrong with the system. It turned out (through trial & error) that the programmer has a software bug where things don't work properly if the CH & HW are set in a certain sequence. Changing the sequence (I can't remember the detail) it works fine.

You programmer looks (from memory) very similar to my son's.

 

[matt1e]

3. The orange wire to the 3 port valve is live when the central heating only is required (it’s used to switch on the boiler. When the hot water is running, this operates the boiler directly via the cylinder thermostat)

I know what you are getting at stem but your above statement can be misleading,
though correct in principal, the orange wire will always measure live whenever the boiler has a demand on it whether it is hot water or central heating if you are metering it while the orange is connected to the system

Matt

 

[stem]

Thanks Matt, you are quite correct. My explanation wasn't very good. In practice, I always remove the orange wire from it's terminal to test it, so that it doesn't get a 'live' fed back from the cylinder stat. Because I do it automatically I guess I forgot to mention it. Thanks for pointing it out, I will try to be more concise in future.