central heating only comes on with h water, stumped engineer

[Dodgemonkey]

My wiring centre has the room stat terminal on its left, positioned vertically, above the "heating valve" terminal, (which in my case is not used). The cable from the room stat comprises just the three - blue, brown and earth wires. The room stat terminal in the wiring centre has four terminals. Working from top to bottom:-

Brown wire to terminal marked 1

Blue wire to terminal marked 2
Earth, or green and yellow wire to terminal marked 3

Between no.1 and no.2 terminals of the block there is another terminal marked with the "E" symbol . This is not used in my case.

On the other side of my wiring centre lies the "mid posn or HW valve" terminal block. This receives the cable from the valve itself, and the cable set up is easy to follow here because the terminal has labels for the cable feed positions. However on my system I noticed that there is no brown wire in the valve cabling, and therefore the terminal marked "brown" is not used.

In summary, cable feed from the valve to its terminal is, top to bottom:

.....grn/yellow (at the top)
.....brown (not used, no cable)
.....grey
.....blue
.....orange
.....white (at the bottom)

Please bear in mind that the wiring positions shown here reflects my set up using Honeywell equipment.

Your room stat cabling has four wires interestingly, so I'd be inclined to make the true earth wire - the green and yellow - into the terminal marked "E", and the common, green wire into terminal four.

I hope this may help.

Mike

 

[bonkersbill]

Live wires are
Room stat, CH, HW, all off- grey
R S on, CH, HW off-grey
R S off, CH on-grey
R S on, HW on, HW off-orange and connected brown
R S on, CH on, HW off-grey, white&brown,orange and connected brown
R S, CH, HW all on-grey, white&brown,orange and connected brown

Recap, HW works perfectly, valve position vertical,
when CH is put on on its own, sometimes the boiler starts up but then turns off after 30secs to a minute,valve position horizontal,
HW & CH on both work though i think the HW is possibly getting too hot, valve diagonal mid position
Valve turns easily and the danfoss moves to all correct positions, the spring works and its only when in the horizontal position that CH doesnt work.

i installed new Room Stat, Program Timer, and danfoss actuator in the hope of curing the problem with no change.

The only thing i have done that has made any difference was after thinking about everything i had done to the system i realised that before i started moving the hot water tank, i had removed a radiator and connected the 2 ends together, this i think meant when HW & CH were on the CH was being sent back through the return too quickly, this meant rads weren't very hot, i put a valve between the 2 ends and now i get red hot rads.

i had the problem before i moved the tank but i didnt know it because the HW was set to come on when ever the CH came on, i noticed problems when i reduced the HW times whilst trying to save money on bills

3 engineers have checked it out thoroughly and cant find a problem, short of them all being useless and the above wires are live when they should be and valve positions are correct, what is left that could be wrong?

 

[bonkersbill]

i'm using honeywell st9400c timer, hoeywell roomstat, danfoss hsa3 actuater and danfoss wb 12 wiring centre,
Room stat brown (Pos 1) becomes live when CH is turned on, when RS is turned up the green (Pos 3) wire becomes live too

 

[MANDATE]

Bill, Those will not be two earth wires!
The wire going to a switch is a 'live' the wire leaving the switch to go to the valve is called a 'switched live'
You have to remember that a switch is just a switch and not an electrcal 'load' like a lamp or a motor.
The wire that leaves a 'load' is a neutral.
In your room stat there will be s small heating element 'compensator' which is a 'load' so your stat comprises both a 'switch' and a 'load'
So the wires will be.
A 'live' from programmer
A 'switched live' to motorised valve ( that completes the switching bit)
A 'neutral' from the stats compensator ( this completes the circuit for the compensator to function)
A 'earth' wire ( for safety but not part of the functioning)
Live wires normally red. Neutral wires normally blue earth wires green/yellow or green.
Switched live wires should be red but could be anything providing it has a red sleeve to indicate its 'possible live'.
You can't rely on colours alone and in your case the two wires with green are causing confusion.
I would think the green/yellow is most likely to be the earth.
I think the plain green is most likely to be the 'switched live' which the other end would lead to the motorised valve. ( red sleeves maybe)
With stat turned down there is only 1 wire live (so easy to identify)
With stat turned up a 2nd wire becomes live (switched live)
I doubt if your problem is related to the room stat but no harm done in checking it out.
I think it more likely to be motorised valve related and divides into either the valve head itself with its motor and micro switches. Or if the system has never functioned correctly, then the wiring could well be at fault.

You really need to understand how the valve head functions, before you can recognize what is not happening that should.
As you have already noticed the valve does not always return to HW position when CH and HW are off.
To have CH only you have to (a) have the valve in the correct position and (b) fire up the boiler)
(a) is achieved by power to the grey wire of valve ( if that power is not there then valve does not move on from mid position and even if it is there a faulty micro switch could still prevent movement))
(b) is achieved by the triggering of a micro switch (if contacts not made due to dirt/burned then boiler dont fire)
When heating is satisfied the room stat switches off the power to the valves orange wire so boiler stops, but the valve does not move cause the power to grey is still there and the motor is still energised holding the valve against its stop.
One of the main problems relating to the wiring is the supply of power to the grey wire, because there has to be two sources ( ie cylinder stat and prorammer HW OFF) Sometimes one of these is missing, making it more confusing (sometimes works sometimes not, depending what is switched on and what demands have been satisfied.
I sure what colour wires you have on your valve, but modern valves have white (from room stat to cover first half of movement
grey (from cylinder stat and programmer HW OFF to cover last half of movement)
orange (from valve to fire up boiler, (this is a switched live))
blue ( neutral)
green/yellow (earth)

 

[Agile]

Thanks all for taking an interest, i agree about not paying if not fixed but after spending 2 hours trying to find the problem and finding out what does work has helped me get to grips with what i can do to find the problem my self, i did not think £20 was bad for a call out.

Thanks for your input Dodgemonkey, i have taken the room stat cover off and there are 4 wires, live to No 1, neutral to 2, i guess an earth to 3 (green) and a definate earth (green stripped) to the earth, do i take it you had both that look like earths connected to the earth?

Even so, there should have been no charge if he was unable to solve your problem. Although a tip of £20 to cover his expenses would be a nice gesture.

When you have wiring using different colours which are not normally used for the purpose the loose ends should have been identified with different coloured tapes.

Tony

 

[bonkersbill]

Room stat appears ok, brown is live and the green becomes live, the green striped is unmistakenably earth.

The grey is always live except when HW only is on, then orange is live,
CH on-grey, orange, white/brown are live, turn Stat down only grey is live, this is regardless of whether the boiler is on or has turned its self off ,i think this suggests that the power is coming on and off when it should, the power is turning the boiler on most times as and when it should but for some reason the boiler is turning its self off even though theres still power to grey, orange, white/brown wires, if this is correct then this is where the engineers are having the problem, all the wires have power when they should but some thing is turning the boiler off, is there a wire that either becomes live or unlive that signals the boiler to turn off that i can run a check on, failing that what reasons are there for the boiler turning its self off when CH only is on, if HW is also on there is no problem, could there be a pressure switch in the boiler or something similar that tells the boiler to shut down?

 

[jackthom]

You could try reinstalling the wire link (internal in the boiler PCB ) that holds the boiler on permanently while running the external system in the CH only mode.

If the boiler keeps running the problem is with the external controls. (As the DHW runs OK this is almost certainly the case.)

A cheap multimeter would be much better than the mains tester screwdriver for checking voltages. Then you could be sure that the orange lead was at the full 230V and not struggling at a lower voltage due to a possibly faulty microswitch or wiring.

 

[Agile]

Exactly, a neon screwdriver is NOT suitable for boiler fault finding.

You need to monitor the voltage on the boler call for heat terminal and see if its drops off unexpectedly.

Tony

 

[bonkersbill]

i will invest in a meter and will check the power from all the live wires in all modes, if these are ok i will have a look at reinstalling the wire link though i think i will need more info as to where to find it or what it looks like and maybe how you reinstall it as i have never seen the boiler.

Please dont anyone quote i need a good engineer, if i get to the bottom of why its not working and its beyond me to fix it, i will then get a 4th engineer to look at what ive found, had enough of engineers fumbleing around the same problem without any answers, at least here ive got a dozen or so looking at the problem.

 

[Dodgemonkey]

Sorry to throw a spanner into this mindbender, but you mentioned that the CH only works more or less normally with HW selected, and when CH only is selected it's only on for 30 secs or so.
I'm wondering whether there's a flow problem around the heating circuit, which is being compensated for by the HW circuit when both are selected. It may be that primary flow is increased through the HW circuit as a result of its laboured route around the heating circuit.
You also mention that HW gets too hot, it shouldn't go higher than 60C, and this may be a result of increased flow of primary through the hot water cylinder whilst the circulating pump is on overrun, but this is speculative.
Satisfy yourself that there is an unobstructed flow around the circuit if you can; check your rads are balanced - about 10C drop between flow and return pipework at each rad; check your final return to the boiler return leg is from the hot water cylinder. Finally, check you have a bypass valve fitted.

 

[MANDATE]

If we take it the valve is not at fault, then the contribution put by dodgemonkey is a feasible explanation.
I can see how when both HW and CH are selected and in demand, then both HW and CH are sharing the flow and if the heating side has partial blockage and restricted flow it may well cope as long as there is a good flow through the HW side. With CH only there is no flow through HW and a partial blockage means no easy escape route. Heat build up, boiler stat kicks in.
Even with HW and CH selected, they only get the water shared until one of the demands is satisfied and this is usually the HW, so the valve moves to CH which means its the same as CH only even though HW is on and satisfied.
There is also the pump to consider. Based on a past problem where hot water was not reaching a distant radiator, the pump was removed for examination. The inlet and outlet ports normally about 20mm diam were scaled up so much it left about 8mm diam ports. (cured problem with new pump) Just thinking if water cannot flow through pump fast enough would this be sufficient to make difference between CH and CH with HW.

 

[bonkersbill]

i've checked the voltage and CH only all lives are 241, HW only 241, CH & HW orange & White/brown are 242/243, grey 142, if these are correct then it looks like either flow or electrics at the boiler unless any other suggestions not mentioned arise.

i went to plumbers to get something to measure the temp at rads but they did not know of any plumbers tool other than a thermometer which they dont have, while there i got talking to an engineer who says hes sure its a flow problem, most likely the return is either teed in the wrong place or teed twice, hes coming to look on monday.

 

[bonkersbill]

My 4th engineer who i thought was coming out to try and fix my problem took a look and said he THINKS it will have 2 tees in the return pipe and the only way to find out is to rip up all the floor boards and follow the pipes to see if there are. There must be another way to find out if it is teed twice on the return, some test i can carry out like putting a valve in some where to see if it keeps circulating.

All this of coarse depends on whether it is teed twice or is there any other reasons why the boiler would shut down when CH only is on.
What i dont understand is why are all my Rads getting hot if there is another T when HW is on at the same time, surely if there is another T it would take a different route and why does it work when HW is on?

Clearly i need to investigate more before i start pulling wardrobes out ,ripping chimney breast conduites open, and carpets and flooring up.
I would be grateful for any more ideas, cheers.

 

[jackthom]

I've been re-reading the thread and can't see a mention of the boiler type which might help.

When it cuts out after a short spell of CH only, is the flow pipe coming out of the boiler stonking hot and is there any temperature or warning display on the boiler ?

 

[bonkersbill]

It says on the fire Baxi Bermuda inset 2, the only lights i can see says boiler lock out light which is not visable unless you remove the bottom of the fire. i cant get to the out pipe of the boiler but the rads are very hot when HW is running as well.