Worcester Heat Slave 12/14 Problems

[Adrian Watson]

Hi

I have the above oil fired Central Heat/Water heating system. I get it serviced each year but it is not due again for another 6 months so hoped someone could give some help on the following.

I am an Engineer so capable to handle moderate DIY jobs and have fixed problems on the boiler before but not sure where to look on this one.

I have a dual channel controller on the system - a proper Worcester one.

With the Central Heating set to off, When I turn the Hot Water to ON the light comes on but no relay clicks/noises and certainly no hot water heating etc.

If I then turn the Central Heating to ON the light also comes on and again no clicks/noises.

It is only when both Hot Water set to ON and Central Heating set to ON and then I turn the Central Heating to OFF (light off) that the system fires up and starts heating water. To stop the water heating I have to turn the Hot Water to OFF. Obviously when up to temp it might stop on its own. This is the only way I can get it to fire up.

Temp thermostats on front of unit are up high as is the room stat so heating should be called for.

I had the same problem (I cant remember exact symptoms) when the chap serviced the system and he said the Controller was faulty and would cost £150+. So I have got a non Worcester controller and wired that up and get exactly the same results. So I think the Controller is not at fault.

Could it be the Control Board that houses the relays that is fault? Dodgy relay?

If someone could give me a few ideas where to look that would be great as don't really want to pay for the Engineer to come back and am sure if I call him he wont remember the fault in detail. I have searched the forums on this but it is difficult to search on such a strange symptom.

Please be gentle... and many thanks in advance.

 

[Terrywookfit]

Ten minutes with a multimeter and circuit diagram will pinpoint the problem.
Does running a hot tap have any effect.

 

[snb]

Check diverter valve

 

[Adrian Watson]

Thanks for the replies...

When I run the hot water tap I hear the flow switch relay click in. I need to try it again with the controller set to water and see if the system fires up, once the hot water is used up.

I just had another play with it and found slightly different symptoms with the original Worcester Controller attached. Possibly my mistake or different with the new controller.

The only way to get the system to fire up is to have both water and Central heating in the ON positions with LEDs lit. At this point it wont fire up until either the water or heating is changed to off. At least it is consistant for both heating and water which makes more sense to me.

To me the system should fire up when either or both water or central heating is in the position with LEDs lit. It should not need the other side to turn off before it fires up.

I will get the meter out this week and use the circuit diagrams to check if the relays are firing correctly. Thanks for the suggestion Terrywookfit.

Thanks also for the suggestion of the diverter valve - snb. I can have a look at it as know it is a common problem.

Any other suggestions gratefully received...

 

[oilhead]

Check the outputs from the programmer at the junction block. I've had these do silly things. As Terry says, 10 mins with a multimeter will sort it out.

 

[Adrian Watson]

Thanks for the reply 'Oilhead' - I will check the output etc as Terry suggested. I will be a few days as dont want to play around with it too much in this cold weather...

 

[Adrian Watson]

Hiya

I have been doing some more investigations on this problem this morning:

I connected the Worcester Controller as follows:
Live & Neutral from the Central Heating System to the Controller
Central Heating & Hot Water returns from Controller to terminal blocks so I could measure the return voltages

Room thermostat set high so demanding heat
Hot and cold water temperature controls set high so demanding heat

The only time I could get a voltage (and hear the relay click) out of the controller was when both hot water and central heating set to 'ON' (with lights on) then turn the other channel 'OFF'. This was for repeatable for both central heating and hot water.

I would expect a voltage from the central heating when ever the central heating was set to 'ON' with the light on.
Same for the hot water.

I connected up a Lifestyle LP722, 2 channel central heating controller the same way and got exactly the same results. The controller came from my brother and was working when he had it installed. It has a jumper on the back set to 'P' which I think is for 'Pumped' system.

It seems a bit strange that both controllers are acting ths same way, so wondered if anyone had any ideas on this?

The Central Heating system should not be able to feedback and damage the Controller due to the relays.

Any thoughts gratefully accepted as I am thinking of buying another Controller.

Many thanks in advance...

 

[Terrywookfit]

Are you getting mains voltage on T3 and T4 on programmer, Test separately.....W on H on Hw & H on.

If not, remove prog and fit a link from L to w on and see what happens. Repeat with H on.

 

[oilhead]

As Terry says, replicate the programmer with links. I have had this situation with Worcester programmers in the past.

 

[Adrian Watson]

Hi Terry and Oilhead

Many thanks for taking the time to reply.

I can try this tomorrow although think I may have already indirectly done what you are suggsting.

I had the two return wires terminating in a terminal strip so I could measure the voltages when the HW and CH were meant to be ON. To recap I saw the voltages only after both HW and CH were ON and either the HW or CH were turned OFF. If I turned the HW OFF, I saw the voltage on the CH and if the I turned the CH off, I saw the voltage on the HW.

I then reconnected the controller returns to were they should be normally ie connected to the relay board.

I repeated the switching of the CH and HW and the oil boilder fired in the same way as when I was measuring the voltages - as above. So I believe the problem is on the Worcester Controller not firing the relays at the right time - the relays seem to need a trailing edge on the opposing CH or HW channel.

I will try with the jumpers as you suggest and repeat the boilder switching to double check it is as I mention above.

Many thanks again...

 

[oilhead]

You need to isolate the programmer completely. Just put in links on the terminal block.

 

[Adrian Watson]

I have isolated the Programmer by putting in links from 240V to HW then 240V to CH then 240V to HW & CH. I get everything working as they should ie HW and CH firing the boiler.

So problem is definately with the Programmer.

Is there a known problem/fix for the Programmer?

I was thinking of going around all the solder joints and resoldering them. Would be good if anyone knew which joints to specificaly resolder or if anyone knew from experience, not to bother. Looking at the back of the Programmer board (the side visible without taking the board off the Controller housing) there are only a few components on there, a resistor, a couple of capacitors, backup battery etc. The chip must be on the other side.

Plan B is to buy another 2 Channel Controller that uses the standard backplate / 4 wire system (L/N/HW return /CH return). I can get a new Lifestyle LP722 for £40 but wondered if anyone could recommend anything else that is cheaper?

Thanks again...

 

[oilhead]

The LP722 for £40 is good. From experience, don't try the Flomasta from Screwfix. I put one in for a customer, changed it for another as it went faulty after 2 weeks, the replacement failed 2 weeks later. I than installed an LP.

 

[Adrian Watson]

Thanks for the advice Oilhead...

Just to recap my findings and thoughts on all this for people looking with a similar problem in the future.

The Control Board has two relays on it (Takamisawn LZ-24HS) that are powered by 24V when the software says to start the Hot Water or Central Heating. These relays bring in 240V to return to the Central Heating relay board. The problem is that there isnt enough power in the 24V side to actually energise the relays. It takes both to be driven on (even though they wont actually activate yet) and then either the central Heating or HW to be turned off to (probably) cause a spike in power to allow the relay to energise. The hard part is moving the relays - once in position it doesnt take much power to keep them energised.

The lack of power could be due to the relay deteriorating, a solder joint somewhere drying out or a component such as a capacitor drying out - all time / age related.

The problem is that the low voltage 24V circuitry is very fine on the board and very hard to test for voltages as you can only see the back of the board when the Controller is connected to the buttons/screen.

I started going down this route but then decided spending £30 on a Drayton Controller was better than spending hours fault finding.

You can get an LP722 for £40 on ebay and a LP522 for £30 - the difference being if you want different time period each day (722) or just for week time and weekends (522).

I fitted it by completely removing the Worcester Programmer leaving a slot just bigger then a double socket. I used a single gang light switch back box - I think it is around 70mm deep and mounted that in the slot left from the Programmer. The back plate that comes with the new Controller will fit the single gang back box. The depth of the back box should be enough that the new Controller sits out clear of the slot - for access. I used 4 cores to connect to the Live/Neutral/CH/HW to the relay board of the Central Heating system. The old Worcester Controller will have the 4 way white plug needed for the connection. Alternatively fit the new Controller to the wall and wire to it using suitable flex.

OK the new Controller doesnt fit sleekly on the Central Heating system unit but I never look at it except when to change the times etc.


So problem solved for £30 -£40 and a little time.

I take no responsibility for the information contained here - you make any mods at your own risk. If in doubt get a professional Heating Engineer in (perhaps the new Programmer first so they have something to fit without having to return).

I had exactly the same symptoms to my Worcester Programmer problems with a second hand Drayton LP722 - probably works the same way and has the same aging faults. Hence always but a new Controller rather than second hand.