Better diagnosing a "no central heating but working hot water" problem

[Edan]

I'm trying to learn a few things while attempting to do some basic diagnosis of what may have caused a problem with my central heating.

I have a Glowworm flexicom 15hx gas boiler for hot water and central heating, with a Drayton LP241 programmer/controller.
These heat my hot water just fine. However, recently, my central heating has stopped working; when the controller enables central heating, the boiler does not fire up.
I also notice that, with the controller's central heating on/enabled, the room thermostat (Drayton RTS1 230V mains) has no click in any position.

I understand that this thermostat needs 230V mains AC power and so have measured the voltage across the live and neutral terminals on the thermostat's wall mount. When the controller sets the central heating on and lights up the central heating indicator, my multimeter's AC voltage reading shows 241V across the live and neutral terminals. When the controller sets central heating off, I read 13V across the same live-neutral terminals (is this to be expected or the sign of a problem?).

The controller/programmer's data sheet (https://www.draytoncontrols.co.uk/sites/default/files/2812_D41-11_LP & LPSi Data Sheet.pdf) has the following wiring schematics, which I'll admit to knowing very little about -

Initially, I also just checked some basic things like my house main fuse box, which has no fuses tripped.
There's a wall switch with the 3A fuse, next to the heating and hot water controller. Turning this off turns off all power to both the controller and the gas boiler (at least the boiler's LCD display goes off).
I don't think there's a problem with that switch's 3A fuse; It's still working, otherwise the controller and boiler's display would be off, right?
The boiler doesn't show any error codes either.
The central heating pressure is reading the same as always (around 1.2 bar).

A replacement room thermostat is £16, so I went and bought a new one (same model) and put it on the same wall mount plate. Then, with the programmer/controller enabling central heating, I noticed that this thermostat now did have a demand click, only the boiler still wouldn't fire up, yet it still fires up when the controller enables hot water.

However, a day later, still with the new thermostat fitted, I again turn the central heating on and go to waggle the thermostat dial and notice it now has no click in any position, which is a bit puzzling. I take it off and still measure 241V across live-neutral (when the controller sets C.H. on; 13V when off). Should I be able to test if the new thermostat has inexplicably broken within a day or is still working by (carefully) connecting it to a normal mains power socket and checking that it clicks?

I did find some diagnostic pages in my boiler's installation manual -

This would lead me to 'Consult the state list' (although I'm now not sure if the new thermostat is correctly signalling), but when accessing the state list, my boiler flashes 'S 30', which isn't mentioned anywhere, as far as I can see. What does S 30 mean?

I've now run out of my very limited knolwedge and ideas.

I'm wondering if there could be a problem with the thermostat's connections to the terminals on the back plate: Can I bypass a problematic thermostat or wiring and simply wire the thermostat's 'live' to 'call/3' terminals to just always signal demand?

Then, even with the thermostat circuit always signalling demand, if the central heating still doesn't fire up, where would that leave a problem?
Could I, for example, hard wire the room thermostat demand signal right on the programmer/controller's back-plate terminals, eliminating/reducing a wiring problem somewhere on the way to the room thermostat circuit?
Or perhaps I've misunderstood things and maybe the thermostat demand signal is combined with the controller's central heating on/enabled signal within the flexicom boiler's electronics itself.
Although it's something I think is almost certainly not somewhere I'm prepared to go, I was still wondering if it's even technically possible to entirely eliminate both the controller and thermostat from consideration by (temporarily) connecting some central heating demand terminals in the boiler's electronics box.

Also, at this point, given that the boiler fires up for hot water OK, who, out of an electrician or gas boiler engineer, would tend to be best suited to further investigate and fix this issue?

Finally, is there anything else you can suggest I look at or try?

 

[ianmcd]

Do you have S plan or Y plan ?

 

[Edan]

Hi Ian. I'm afraid I don't know the answer to that; those are new terms to me.

From what I can see, the distinction is whether there's one 3-port valve serving both hot water and heating circuits vs two 2-port valves, one for each of the hot water and heating circuits, but otherwise, they both have a single room thermostat and a single hot water cylinder thermostat.
If that's right, well then at least I've learned one new thing today, but otherwise I don't know the answer, even after looking through my boiler manual , which does not use either term, as far as I can see.

 

[terryplumb]

Is it Y plan that you have with a 3 port valve? If so,
it's probably that that isn't functioning

 

[Harry Bloomfield]

3-port valve serving both hot water and heating circuits vs two 2-port valves, one for each of the hot water and heating circuits, but otherwise, they both have a single room thermostat and a single hot water cylinder thermostat.

Find the valve(s), probably in your airing cupboard. An electrical actuator box, operating a the actual valve underneath it. A 2-port will have a pipe either side of it, a 3-port will be similar to that, but with a third pipe, dropping down at right angles to the other two, forming a T.

You may find that by giving the valve a sharp tap, with the wall stat calling for heat, it is enough to free it up to work again for a while.

 

[Edan]

Ah, so these valves (whether Y or S plan) all live with the water tank, not within the gas boiler unit itself then? I assumed it'd be part of the gas boiler.

My water tank and accompanying piping appear to have two of these motorized valves -

at the highlighted locations -

and according to this system's manual, the one of the right controls the "Flow to rad circuit" (on pg. 30).

I also tried turning on the central heating at the programmer and giving it (the valve on the right) as sharp a tap as I dare, without success. So, I had no idea this could be a possibility at all, but are you hinting at: If this valve to the radiator circuit is stuck or otherwise broken, then would that also account for the room thermostat not actually getting powered up with the required 230V AC needed to signal demand, even when the programmer/controller turns on the central heating? Or might the room thermostat's determined refusal to 'click' and signal demand in any position (even with a brand new replacement) be just a confusing red herring that might also be a problem, but is unaffected by a possible radiator circuit valve problem?

 

[Harry Bloomfield]

If this valve to the radiator circuit is stuck or otherwise broken, then would that also account for the room thermostat not actually getting powered up with the required 230V AC needed to signal demand, even when the programmer/controller turns on the central heating? Or might the room thermostat's determined refusal to 'click' and signal demand in any position (even with a brand new replacement) be just a confusing red herring that might also be a problem, but is unaffected by a possible radiator circuit valve problem?

The stat signals the valve, the valve, once it has moved to open, then signals the boiler to run.

 

[terryplumb]

You would need to do voltage testing at the wiring centre to establish if the stat is energising the valve. If the valve is receiving voltage from the stat ,and isn't moving that's your problem, possibly a failed motor.

 

[CBW]

S30 is a status code, which means it’s waiting for the room thermostat for demand, however the thermostat won’t likely be wired up directly to the boiler. When testing, you need to test the switch live, so between neutral and 3, but if your new one isn’t firing the boiler, then it’s likely to be the Honeywell 2 port. If you remove the head, or latch the metal lever into the manual position, you can have a little heat when requesting hot water.

 

[Johntheo5]

The roomstat should make a click every time you change the setting up and down around the room temperature, is it doing this?, if so, turn it right down to minimum and when you pull the manual lever on the side of the 2 port valve you should feel a reasonably stiff resistance while pulling it. Now turn the roomstat fully clockwise or until you hear a click and if the 2 port valve has now opened then there will be no resistance to pulling on the lever and the problem is somewhere else, possibly in the 2 port valve end switch that fires the boiler.

Also......
"I understand that this thermostat needs 230V mains AC power and so have measured the voltage across the live and neutral terminals on the thermostat's wall mount. When the controller sets the central heating on and lights up the central heating indicator, my multimeter's AC voltage reading shows 241V across the live and neutral terminals. When the controller sets central heating off, I read 13V across the same live-neutral terminals (is this to be expected or the sign of a problem?)."

Once the CH is programmed on then there will allways be 240V between L &N, but ony 240V between terminal 3 and N when the stat is calling for heat or you turn it up and it clicks.

 

[Edan]

"The roomstat should make a click every time you change the setting up and down around the room temperature, is it doing this?": No it isn't. The only time I've had the room thermostat give me a click since investigating this problem was when I bought a brand new replacement and fitted it. Then, when putting the central heating on at the programmer, I twiddled the thermostat dial and got consistent clicks around the expected temperature marking, but still no boiler fire-up. I retried this all again the following day and no clicks any more.

"When testing, you need to test the switch live, so between neutral and 3": Oh, I wasn't aware that this would be relevant; I thought the thermostat's wiring schematic shows it just completes the connection between L and 3 (when above the set temp.), across which I should expect around 230V.
I have again multi-metered the room thermostat terminals and read 240V across L-N and 215V across L-3/call (only when the programmer's C.H. is set to on).
My meter reads 15V across N-3 with the programmer's central heating on.

"If the valve is receiving voltage from the stat, and isn't moving that's your problem, possibly a failed motor.": I tried moving the radiator circuit valve to manual (with the programmer central heating on) and still nothing.

I wonder if there's a couple of problems happening at the same time and whether I can reduce or eliminate one issue from the investigation.
For example, would it be reasonable to hard-wire the thermostat wall terminals to always 'call' and so remove from the equation a loose/weak thermostat pin-to-contact connection or even an inexplicable doubly broken thermostat? Would a hard-wired L-to-3 be a permanent call to heat (or would that be more a palm to forehead situation )?
If that sounds reasonable, then I can retry setting the radiator valve back to manual when the programmer's central heating is on and see what happens.

So, if that fires up the boiler, then it all looks like either a bad (pair of) thermostat(s) or bad wiring/contacts between the wall plate and the thermostat pins.
However, if that still doesn't fire up the boiler, then I can go and re-check the boiler's state display (to see if it's still indicating 'S30' or something else) and then may have to figure out where else I should check voltages.

 

[terryplumb]

Manually latching the valve open will not fire the boiler,only open the gate in the valve body to allow water to flow through it.
As I said ,you need to do voltage testing at the wiring centre to establish what the fault is.
If you don't know what to check or how it's probably time to call in an engineer.

 

[Johntheo5]

I would start at the "no click" switch, disconnect the wires, there should be infinite resistance, M.meter reading l, with switch turned down, probes between terminals L&3 and should read 0 or close to it with switch turned up. If not, stat knackered, would seem strange for a new switch though.

 

[Harry Bloomfield]

I would start at the "no click" switch,

Depending upon the range of the stat, the lack of click - might be due to it being very cold where the stat is located, that the stat is remaining on.

 

[Johntheo5]

Post #1 shows a range of 10C to 30C so if room temp < 10C then stat On.