Thermostat or Programmer?

What type of boiler do you have? What type of system do you have? Have you got a hot water cylinder? do you have a 3 port valve? do you have 2 two port valves? Much more info needed before any help can be given. Why do you suspect the programmer over any of the other controls?

 

Jay Dubb, you say "current is coming through to the thermostat as it should" so surely that means your programmer is working chust fine?

Do you have a volt meter/ test meter?

 

Sounds like a faulty port valve.

 

JW, can you confirm that 'live' power appears at Term 1 only when your CH programmer goes 'on'?

Can you further confirm that Term 3 only becomes 'live' when you turn your room 'stat up beyond it going 'click' and T3 goes 'dead' when you turn the 'stat back down?

In which case it looks as tho' both your prog and 'stat are fine (assuming the Neutrals are also working).

Ok, you mustn't muck around with your system too much 'cos it's well pressurised. But, can you identify the two separate 2-port valves in your system? They are both in that pic of yours.

If so, get someone to turn on your DHW ("I luuuvvv you, hot water"), and see what the HW valve does - it's the one with the pipe goign down and into that huge white cylinder thing with the 'Sentinel X100' label on it..

It should go 'whirrrrr' followed in a few seconds with a 'click'. Does it? Awesome.

Now turn off your DHW at the programmer and turn on your CH there instead. Make sure the room 'stat is calling for heat too.

Does the other 2-port valve do the same as t'other one?

Report back, pleeeeeez.

 

Cool. That one is your DHW.

The other one - that doesn't work - is the CH one.

Make and model of that valve?

Ok, without killing yourself, prise off the white cover of the other one - and report back.

Bearing in mind that, even if the timer/room stat ain't calling for heat, that valve may still have a live feed.

Tell us the wire colours, pleeeeeeez.

(Have you tried manually moving that switch on the end - on the other one? In theory that should fire up the boiler and deliver hot water to your rads.)

 

Range SZM 1802 - possibly now 'Sunvic'.

A quick Google suggests they ain't reliable.

If the 'head' can be replaced, then that's something you can do yourself - just swap each wire as per the original.

If the whole thing needs replacing, then perhaps best to go for a better make such as Honeywell (that's the advice I found.)

Ok, if the cover doesn't come off to allow you to look inside and take readings, then you can go back to the wiring centre and work out which wires as the ones going to this fellow.

Looks like it should be brown, blue, orange and grey.

Blue is a permanent Neutral. Brown should become live when the timer goes 'on' and the room stat says 'heat, please'. That should get the motor running. Head out on the highw.... oops, sorry .

Grey is probably permanently live and feeds the microswitch, and orange becomes live when the microswitch is tripped - ie when the valve opens.

Anyways, it's almost certainly kaput so you need to replace just the head (you can do this) or the whole valve (best left to a pro since it's an unvented system.

Surf for that valve type, and add 'head replacement' or similar to your search.

 

How can you tell betwixt head and valve? Dunno - probably by replacing the head first...

Or, I guess if it all seems to be 'stuck', it could be the valve. But if things just ain't happening at all - or if it does move but the boiler still doesn't turn on - it'll likely be the head (the electrical bit).

Most likely it's the head.

Yours isn't just a sealed system like a combi boiler, but a proper pressurised jobbie and I understand that for this you need special qualifications to install and work on them. That's all I know.

However, the pipework part involving the valve would seems to me to be fairly conventional, and if you were competent you could probably replace the whole valve no problem.

But I couldn't possibly suggest you do that...

 

Drain the system down and replace the whole valve.

 

JW, it is - as you suspect - a very easy item to replace in normal circumstances - release pressure via DoC until no more water flows oot, and get ready with a pan and cloths when you slacken off the 3 nuts.

The nut threads will be the same on the new valve, so you don't have to remove the old nuts and olives from the pipes - phew. Just make sure the pipe ends are clean, and add a smear of jointing compound over the olive and also on the male threads of the new valve - this will make tightening a smoother task. (Don't get any compound inside the pipe...)

The wiring can be done afterwards, note carefully where each wire goes in the wiring centre. DON'T get mixed up there...

Make sure the valve faces the right way - I'm guessing it's directional.

Ok, what I have NO idea about, is which DoC you use, and how you top up the system again. I have NO experience with this type of system (only combis which are much more straight-forward.)

I'm pretty sure there will be no safety issues provided you don't touch the 'other' side of the system; ie the pressurised supply to the taps. Make absolutely sure you know what you are doing - there are 2 pressure vessels there, for instance, and I think only one of them is on the side you will be messing with, and I think that's the red one with the gauge...

Right, what are the operative words above? Correct - "I think", "I'm pretty sure", "I'm guessing...". So - chust make bludy sure you know what you are doing first and certainly don't take anything I've said with any confidence...

 

Sorry if i sound a bit antagonistic, but you have issues that are difficult to diagnose online, just get someone in, it will save a whole lot of messing about trying this and trying that, whereas any decent engineer will be able to test and diagnose and repair your fault quickly and without the expense of trial by error.