Hot water from central heating?

[gencouple]

Apologies if this issue has been posed before, although I could not find it in the first 20 threads.

Simply, I have noticed my domestic hot water heats up when my central heating is turned on, this, despite hot water not being selected on the boilers inbuilt programmer?
The boiler incidentally is a 15 year old, oil fired Worecester Danesmoor 20/25. Its a conventional 'old type boiler' (not condensing) and this issue aside, it works very well.
If I select hot water via the boilers in-built programmer the water becomes very hot as opposed to the very much reduced temperature I get when only the central heating has been selected.
I suspect the hot water tank is being topped up by my running the central heating though question why it would do this? This leads me to my question which is; Is it normal for my hot water be warmed (albeit slightly) by having the central heating on, and if not, does this indicate something is going on in the background which should not be doing so.
To give you some idea to what extent the domestic hot water is being heated, it is certainly warm enough to wash in comfortably.

About two weeks ago following a powergrid loss - when electricity was restored some 15hrs later, I noticed the boilers programmer lcd has disappeared. I traced that fault to a spent battery on the back of the pcb which I replaced. Whether that has impacted on something I'm unsure, though this issue with the domestic hot water seems to have begun around the same time?

Reading previous invaluable advice on the forum had me wondering if the C/H systems 3 port diverter may be suspect?
Any pointers or thoughts with this issue would be very much appreciated.
Thanks in advance

 

[flameport]

If it a recent problem, then a failed valve is certainly likely, possibly sticking.
If it has always done it since the system was installed, then circulation other than via the valve is a possibility.
If you turn on the heating only, then check the pipes from the valve, only the inlet and heating outlet should get hot - if the hot water outlet also gets warm/hot then the valve is the fault.
The head is usually removable, leaving just the valve spindle underneath which can be turned with pliers, this will determine if it is just the head/motor or whether the actual mechanical valve has failed internally.

 

[gencouple]

Sound advice flameport and many thanks for it. I will give the spindle a twist and see how free it is (or not)
I will let you know how things go - Many thanks for your time

 

[ericmark]

With my daughters old house some one had latched the motorised valve onto bleed position when a micro-switch inside the valve had failed, it does seem micro-switches do fail causing some unusual faults, and since the internal wiring of motorised valves is not standard, what happens under fault conditions varies. With my father-in-law it damaged the pump because it ran boiler and pump against a closed valve.

Also we have different plans. Y, C, and W for example, each will show different faults when micro-switches fail.

However you say fault in programmer, now rectified you say, but programmers had both electrical and mechanical switches, I seem to remember in the early C system it used thermo-syphon and no valve so the standard 16 program programmer had a mechanical and electrical switch which turned it into a 12 program programmer. You could not physically or electrically select central heating without domestic hot water.

Maybe you have moved one of the micro-switches inside the programmer? However before anyone can really guide you, you need to state what system is used.

 

[gencouple]

Hi again flameport/ericmark - Some further points following your much appreciated input. Firstly, I have now accessed the spindle which you mention. The spindle does indeed turn by hand albeit only by a few degrees. See attached file showing the spindle at its two most extended positions. Feeling the apparently limited travel of the spindle may be being prevented from opening further, I took a small pair of pliers and with a bit more force tried moving the spindle further but nothing dislodged allowing for further travel. Unless you guys report that the spindle should travel further, I'm inclined to feel the spindle is working okay?

Whilst the motorised head was removed, I took the opportunity of looking inside to see if any bits of broken cogs or springs were present. All appeared as it should. However, prior to removing the head, I had learnt previously from a youtube clip about checking the manual lever on the head for resistance then watching to see if the lever returned from manual position to auto. This it did regardless how many times I tried it. (At that point, I felt happy that at least something was doing what it was supposed to) Now, with the head removed from the spindle and with access to view inside the head, I moved the lever to watch as the gears meshed and springs operate. This worked fine and I saw how the two points engaged with the micro switches just as it had on the youtube clips I had watched. Satisfied all was good, I began replacing the head to the spindle.
Recalling a youtubers advice, as I gently aligned the head to the spindle, I moved the lever from auto to manual. (This as you will probably already know, the better to allow the spindle to locate and align itself without undue force or incorrect seating) Now with the units two locking screw in place, I again moved the lever from its auto position to manual expecting the familiar resistance. Nothing! There was no resistance and the lever stayed wherever I left it. Despite being certain I had the head & spindle aligned, I removed it again and could see immediately the contacts were still engaged with the micro switches. I then inserted a screw driver at the point where the spindle locates and turned. Sure enough the gearing worked and the contacts disengaged from the micro switches. The problem which now appears to be the contacts are not backing off from the micro switches - new powerhead? I am unsure if this is the cause of the initial issue or just something to cloud the issue.

Ericmark - Thank you for your thoughts. Your efforts deserve a better answer to your question concerning ''what system is used'' I have uploaded a photo of the heating system located in my bungalows attic but suspect you mean Y C or W of which I haven't a clue? Any pointers to help me. determine which I have. Also aattached is a photo of the boiler itself and its programmer.
Concerning micro switches inside or at the back of the boilers programmer - there does not appear to be any. Following the powercut we had, when power came back on we noticed the boilers lcd had disappeared. I replaced the programmers small 10 pence sized lithium battery and even I was surprised this had the desired effect and the display came back on. Looking back, coincidentally, it was onwards from then this issue began

Cheers lads, over to you .....

 

[gencouple]

PS Domestic hot water temp has risen dramatically from tepid to magma!

New powerhead - Sorted!