Central Heating not working

[andypbarker]

I have a condensing boiler operating both the central heating and the hot water. The hot water is stored in a hot water tank fed from a header tank and the central heating is a sealed system {I think} with a smaller header tank. The boiler will not fire up to only supply central heating. In order to get the heating on we have to run enough hot water out of the tank to convince the boiler to fire up. Bizarrely this also starts the circulation pump and the radiators heat up. As soon as the water in the hot water tank reaches the correct temperature the boiler shuts down and the central heating stops supplying heat to the radiators. I have adjusted the thermostat and have both the hot water and central heating permanently on -- all to no avail. As a possible additional pointer the radiators downstairs heat from the top down so the top is hot and the bottom is cold -- I know this sounds crazy but it is true.

Does anyone have any ideas? please

 

[andypbarker]

Apologies it is not a sealed system rather it is a feed and expansion system and the condensing boiler is an Ideal Classic HE12 Condensing Heating Boiler

 

[OilLecky]

Andy this sound very much like a wiring / electrical control problem. Has the system ever worked correctly? Has anyone worked on it lately? Do you have / can you work an electrical multi-meter or if not are you confident testing for an electrical supply with a test light?
Do you have a circulation pump for hot water and another for heating or is it just one? Do you have any electrically operated 2 way zone valves or 3 way valves?
Give us some info and we can probably help you.

 

[andypbarker]

Thanks for the quick reply oil lecky.

To be honest the system has never worked really as I would expect. It was installed about 2 years ago to replace a back boiler. As i understand it I have a three way valve which is supposed to control the flow of hot water somehow {it seems to me that it is only connected to the heating system and not the hot water} I also have an electrical box which has 20 possible connections on the right hand side as you look at it and 20 on the left. There are 6 wires in total, very thin, and coloured orange / white, blue / white and green / white (2 of each). I don't have a clue as to what this does. My hot water system is gravity fed, I know this because if i hold the shower hose up in the air the pressure falls off, from a hot water storage tank with an immersion heater switch. The boiler is wired to the electrical circuit and has a detached control panel for setting the time and frequency of both the heating and hot water {it is this that makes me think the box with the wires described previously are redundant}.
As far as testing is concerned, i'm happy to have a go with a test light -- I would need help on what to test. Thanks

 

[OilLecky]

Andy, I posted something on your profile. I need to work out how I can send you some information. i.e. a file

 

[OilLecky]

Andy. Your Central Heating / Hot Water programmer has two outputs one to hot water, which you are getting and one to the central heating system. This heating supply should go to your Room thermostat (if you have one) and then to the white wire of the 3 way valve. If you have both hot water and central heating selected the 3 way valve should be in the mid position. ( Take a look it may have an indicator on the side.) When the water in the cylinder is hot enough , the cylinder thermostat should change over and then the 3 way valve should move to hot water only position by a supply from the cylinder thermostat to the grey wire of the 3 way valve. Take a look at the valve with hot water only, hot water and heating and just heating selected and tell us what you see. The supply to the boiler from the hot water system is via the orange wire of the 3 position valve.

 

[OilLecky]

Correction. When the cylinder thermostat changes over because the water is hot enough, the 3 way valve goes to the central heating only position NOT hot water. Sorry!

 

[andypbarker]

OilLecky

Thanks for your response, sorry about the delay, lost internet as well as heating! Not connected to each other! I will check this three way valve first thing tomorrow and repost. One thing I forgot to mention was that all was ok until a power cut last week, however we have never been able to have the central heating on on its own, only ever when the hot water was on.

Once again thanks for your help, will respond tomorrow

Andy

 

[OilLecky]

Andy, Hope that you got somewhere today. It is "fairly normal" to not be able to get heating without hot water selected. The logic behind this is that normally we need hot water all year around and then in the winter we have an additional requirement of central heating. We do not normally need heating without hot water.
If the fault first occurred after a power cut I'd be looking more towards the programmer but you need to do your checks first.

 

[gas4you]

It is "fairly normal" to not be able to get heating without hot water selected.

Not on a modern 'Y' plan that was fitted 2 years ago it isn't Unless the valve is faulty or not wired correctly.

 

[MANDATE]

The valve functions over two sections. First section relies on room stat and white wire (which must be ok, otherwise it could not go to mid position)
The second section relies on power from the 'grey' wire. this is supplied from two sources. (a) the satisfied terminal of the cylinder stat and if HW happens to be switched off then (b) the HW OFF terminal of the programmer. These power sources needs to be checked out first.
It would be no surprise to find a wire missing, especally (b).
If the wiring is found to be correct, the problem will be the valve spindle or more likely the valves actuator head.
There are two requirements that need satisfying. The valve has to move fully across to the CH position, then the boiler has to light.
If it moves across and does not light then problem is micro switch.
If it does not move across, then problem could be other micro switch or the motor.
It is wrong to assume the valve should be in mid position when both HW and CH are both selected. It may be true for a short period, it is designed to change to any of the three positions depending what is in demand and what has been satisfied.
If HW is satisfied and CH is not, then valve will/should move to CH position and trigger the micro switch as it travels.
You obviously get some CH, but that occurs only when there is demand for both CH and HW and because HW is required, the cylinder stat provides the power to light boiler. This situation of course is short lived as your HW will become satisfied and what should happen next is not happening.