Replaced Horstman 527 with Honeywell ST9400c and Hot Water will not fire

[btolsta]

Good morning everyone,

Looking for some pointers. As the title says we replaced the old broken one with a new ST9400C. Transferring the wiring didn't seem too bad at all. I have attached a pic of the old wiring. Basically one wire for CH, one for HW and the loop from Live to 2 and 5 for common. The new wiring was just to drop the loop and wire in the CH to 4 and HW to 3. Tested the programmer and the CH works perfectly on timer\constant\boost. The HW on the other hand will not fire the boiler at all on either timer\constant\boost although it all looks right. So far we have checked the programmer is not part of the faulty batch and also turned off the backlight with no effect. We even tried bypassing the programmer and looping L to 3 and powering up the system so that there is power to HW constantly and it still doesn't fire. Is this looking like a plumbing problem now or am i missing something? Any help would be gratefully received.

G

 

[stem]

What you have done sounds right.

Horstmann terminals were:
Hot Water on = 1
Central heating on = 4

..and the Honeywell
Hot Water on = 3
Central heating on = 4
The live loops are not required as the Honeywell has the links internally.

So, have you checked that the wire to terminal 3 is secure and that the clamp is on the conductor and not the insulation?
Did the system work OK before you changed the programmer? I'm assuming you didn't change it to try and cure this fault.
As a test, if you move the wire from terminal 3 to terminal 4, so that both the heating and hot water wires are in the same terminal, replace the programmer and turn on the central heating, does the hot water come on as well? If it does the programmer is faulty, if it doesn't the fault lies elsewhere.

 

[btolsta]

Stem,

I will give that a try at the weekend. It's a relatives house so will be down there on Saturday. Ty for confirming the wiring for me, always good to have a second opinion on these things! The system was working ok as far as i understood. She had the HW on constant and the CH on a timer with the old programmer. We checked the wiring into terminal 3 on the programmer side as the contact was secure with good contact on the wire. I will give you suggestion a bash tomorrow. Could it be possible that the other side of that HW wire may be the issue as we did pull the cables out from the wall to terminate them in the new backplate?

G

 

[stem]

It does seem odd if the fault only occurred since you swapped the programmer over, which would suggest that something has been disturbed.

I asked the question about the fault being there previously, because sometimes individuals have swapped a programmer thinking it would cure a fault and then when it hasn't asked the question on here, but failed to mention that the fault was already there.

Normally, my first port of call if someone reports the hot water not working would be a motorised valve. The wiring photo you posted would suggest that unless the system is of a very old design that it probably will have two, 2-Port motorised valves. Something like this.

Untitled

• stem
• 26 Mar 2010
• 6

These are more frequently responsible for fault you describe as either the motor or a micro switch inside the valve that operates the boiler can fail. If you find the system does have a motorised valve, and you have a multimeter and can use it safely, a quick check to see if there is 230v across the motorised valves blue and brown wires when the hot water is on would

 

[btolsta]

The system is i would say over 20 years old now anyway so i will have a gander and see what is on the boiler and cylinder side the morrow. Pictures will follow. If that valve was the issue would that stop the oil boiler from firing up?

 

[stem]

If the valve motor has failed then the valve will remain in the closed position. Also, there is a microswitch inside the motorised valve. When the valve winds fully open it operates the microswitch and this is what operates the boiler. So if either the valve motor has failed, or the microswitch, then the boiler won't fire.

 

[btolsta]

Stem,

We tried some stuff while down at the house today with little success. I have attached some pictures of the setup but appreciate you won't be able to tell a lot from them as that's only part of the puzzle. I couldn't find anything that resembled the valve anywhere near the boiler or cylinder. It just had some basic shut off valves and three stats. I min and max for the CH and a white stat for HW I assume. Still no luck getting it to fire. For a sanity check on Monday night we are going to stick the old programmer back on and see what works.

 

[stem]

You may not have motorised valves. Most systems (excluding Combi's) installed from the 1980's onward tend to have them. The three items show in you photographs are strap on pipe thermostats. Usually they are used for frost protection, but I have never seen three installed on the same system. These thermostats must be wired to control something though, the question is what?

Was the system working OK before you changed the programmer? or was it because of this problem that you changed the programmer?

 

[btolsta]

The programmer was working fine. It was just losing its time and programs with power cuts. As a test we are going to put it back in place and see what happens tomorrow night.