Boiler not switching off

[Fordy81]

I'm having problems with my boiler switching on and off constantly when requesting heating or water, but I've now discovered another problem.

When the temperature being requested by the room thermostat is met, the boiler doesn't shut down. It just keeps going until I turn it off by the programmer. Any ideas why this might be?

As a bit of background, when I bought the house I turned everything off for 4 months during renovation so have no idea whether things worked properly before.

I bought a new programmer, which I fitted myself. Moved it slightly so had to reconnect all the wires. 99.9% certain it was done correctly as I tagged each one. I also bought a new digital room thermostat to replace the analogue one, and made two wires, neutral and earth I believe, safe.

I've had a new thermistor in the boiler, and a new pump fitted in trying to rectify previous problems.

Boiler is a Potterton Suprima, E&F tank in the loft, hot water tank in airing cupboard.

 

[D_Hailsham]

More info about the system, please.

Make and model no of all components,except boiler and HW cylinder, will do for a start.

A pic of the cylinder cupboard, so we can see how everything connects together, would also help.

 

[Fordy81]

That's the old pump. New one is a Grundfos.

Thermostat is a HoneywellDT90E

Programmer is a Drayton LP722

Need anything else?

Thanks

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• Fordy81
• 21 Jun 2014
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• Fordy81
• 25 Jun 2014
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• Fordy81
• 25 Jun 2014
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[D_Hailsham]

Thanks for the info & pics.

Which programmer did you have previously?

 

[Fordy81]

Thanks for the info & pics.

Which programmer did you have previously?

It looked identical to the new one but think it was the MKII version

 

[D_Hailsham]

When the problem next occurs, remove the programmer from the backplate and see if the pump stops or continues to run.

If it continues, check the wiring to make sure there are no strands touching adjacent terminals.

If it stops, the new programmer is faulty.

 

[Fordy81]

When the problem next occurs, remove the programmer from the backplate and see if the pump stops or continues to run.

If it continues, check the wiring to make sure there are no strands touching adjacent terminals.

If it stops, the new programmer is faulty.

#

Ok so presumably it should still run? And if the wires all look ok?

 

[Fordy81]

When the problem next occurs, remove the programmer from the backplate and see if the pump stops or continues to run.

If it continues, check the wiring to make sure there are no strands touching adjacent terminals.

If it stops, the new programmer is faulty.

Pump kept running. Checked all the wires and seemed fine. However. I've noticed that I have no wire going in to the terminal point numbered 2. On the back of the programmer this says heating off.

Have I wired it incorrectly? Is this why it isn't switching off?

Edit: Wiring is definitely the same as for the previous programmer. There was no wire to terminal 2 before. I don't know whether it worked before or not though.

 

[D_Hailsham]

Pump kept running. Checked all the wires and seemed fine. However. I've noticed that I have no wire going in to the terminal point numbered 2. On the back of the programmer this says heating off.

Have I wired it incorrectly? Is this why it isn't switching off?

1. No wire required on 2
2, If it continues running when the programmer has been removed, there's a wiring fault after the programmer.

Do you have multimeter (and know how to use it? )

 

[Fordy81]

Pump kept running. Checked all the wires and seemed fine. However. I've noticed that I have no wire going in to the terminal point numbered 2. On the back of the programmer this says heating off.

Have I wired it incorrectly? Is this why it isn't switching off?

1. No wire required on 2
2, If it continues running when the programmer has been removed, there's a wiring fault after the programmer.

Do you have multimeter (and know how to use it? )

Ok cool.

Sorry, bit confused now. So when the programmer is taken off, what should happen? You said if the pump stops it's the programmer that's knackered. But if it carries on the wiring is faulty after it.

I do have one. And no I don't. Is it easy to learn? lol

 

[D_Hailsham]

So when the programmer is taken off, what should happen?

The pump should stop.

The programmer contains two relays, one for HW and the other for CH. When the timer calls for CH, the relay closes and mains voltage (from the L terminal) is applied to terminal 4; and from there it goes to the room stat. Obviously, if the programmer is not fixed to the backplate, no voltage should be on terminal 4.

You said if the pump stops it's the programmer that's knackered. But if it carries on the wiring is faulty after it.

Correct. If CH is turned Off at the programmer there should be no connection between L and 4, so the boiler should stop. If the programmer is removed from the wall and the boiler then stops, it proves that the programmer is providing a connection between L and 4, when it shouldn't.

If the boiler continues to run when the programmer is removed, it means voltage is getting to the boiler from another source. The problem now is finding the source. And that's where the multimeter would be useful.

But as you have no experience of using one we have to go about it another way.

The boiler can be turned on in two ways: by the cylinder stat, or by the motorized valve. We need to find out which as it eliminates a lot of possibilities.

In your opening post you said:

When the temperature being requested by the room thermostat is met, the boiler doesn't shut down. It just keeps going until I turn it off by the programmer.

1. Does this happen when the programmer is set to CH and HW both On, or only when CH is On?

2.When the room stat has reached temp and the boiler continues to run, what happens if you turn the cylinder stat down?

 

[Fordy81]

So when the programmer is taken off, what should happen?

The pump should stop.

The programmer contains two relays, one for HW and the other for CH. When the timer calls for CH, the relay closes and mains voltage (from the L terminal) is applied to terminal 4; and from there it goes to the room stat. Obviously, if the programmer is not fixed to the backplate, no voltage should be on terminal 4.

You said if the pump stops it's the programmer that's knackered. But if it carries on the wiring is faulty after it.

Correct. If CH is turned Off at the programmer there should be no connection between L and 4, so the boiler should stop. If the programmer is removed from the wall and the boiler then stops, it proves that the programmer is providing a connection between L and 4, when it shouldn't.

If the boiler continues to run when the programmer is removed, it means voltage is getting to the boiler from another source. The problem now is finding the source. And that's where the multimeter would be useful.

But as you have no experience of using one we have to go about it another way.

The boiler can be turned on in two ways: by the cylinder stat, or by the motorized valve. We need to find out which as it eliminates a lot of possibilities.

In your opening post you said:

When the temperature being requested by the room thermostat is met, the boiler doesn't shut down. It just keeps going until I turn it off by the programmer.

1. Does this happen when the programmer is set to CH and HW both On, or only when CH is On?

2.When the room stat has reached temp and the boiler continues to run, what happens if you turn the cylinder stat down?

Ok, I'm gonna keep reading this over until I understand. lol

Just to clarify; when the programmer is on CH TIMER, it switches off when it should do (not sure about when it meets requested temp as only set it to come on for 5 mins to test). When the programmer is on CH ON, this is when it doesn't shut down when stat temp is met. When the programmer is set to CH OFF, it is off.

Sorry, confused again. The pump definitely was still running when the programmer was removed. However I'm pretty sure the boiler stopped. Want me to check again for sure?

I did watch a video about using it for voltage. lol I can get my dad round to test it as he knows how to use one.


1. Does this happen when the programmer is set to CH and HW both On, or only when CH is On? This is only when CH is on, as far as I can tell.

2.When the room stat has reached temp and the boiler continues to run, what happens if you turn the cylinder stat down? I have no idea, I'll try this and report back. Do I just turn it right down to the minimum?

 

[D_Hailsham]

Ok, I'm gonna keep reading this over until I understand. lol

Just to clarify; when the programmer is on CH TIMER, it switches off when it should do (not sure about when it meets requested temp as only set it to come on for 5 mins to test). When the programmer is on CH ON, this is when it doesn't shut down when stat temp is met. When the programmer is set to CH OFF, it is off.

Now it's my turn to ask for clarification. Presumably "CH TIMER" means when it is on "Twice or "Once".

Even if the boiler is only set to run for five minutes, you can still check if the room thermostat is working by turning it down (boiler stops) and up (boiler starts).

So the problem only occurs when the programmer is set to (permanently) ON?

The pump definitely was still running when the programmer was removed. However I'm pretty sure the boiler stopped.

Suprima boilers have "pump overrun". This means the pump continues to run for a few minutes afer the boiler goes out. It's to prevent the boiler overheating.

1. Does this happen when the programmer is set to CH and HW both On, or only when CH is On? This is only when CH is on, as far as I can tell.

2.When the room stat has reached temp and the boiler continues to run, what happens if you turn the cylinder stat down? I have no idea, I'll try this and report back. Do I just turn it right down to the minimum?

You really need to try all combinations of programmer positions and thermostat positions to see what happens. Even check the "not so obvious" ones, such as turning a stat up (to max) and down (to minimum) when the programmer is set to Off. You only need to check timed "Once", so there are 3 x 3 x 2 x 2 = 36 possible combinations to check.

I only need those which produce the fault condition.

 

[Fordy81]

Now it's my turn to ask for clarification. Presumably "CH TIMER" means when it is on "Twice or "Once".

Even if the boiler is only set to run for five minutes, you can still check if the room thermostat is working by turning it down (boiler stops) and up (boiler starts).

So the problem only occurs when the programmer is set to (permanently) ON?

The pump definitely was still running when the programmer was removed. However I'm pretty sure the boiler stopped.

Suprima boilers have "pump overrun". This means the pump continues to run for a few minutes afer the boiler goes out. It's to prevent the boiler overheating.

1. Does this happen when the programmer is set to CH and HW both On, or only when CH is On? This is only when CH is on, as far as I can tell.

2.When the room stat has reached temp and the boiler continues to run, what happens if you turn the cylinder stat down? I have no idea, I'll try this and report back. Do I just turn it right down to the minimum?

You really need to try all combinations of programmer positions and thermostat positions to see what happens. Even check the "not so obvious" ones, such as turning a stat up (to max) and down (to minimum) when the programmer is set to Off. You only need to check timed "Once", so there are 3 x 3 x 2 x 2 = 36 possible combinations to check.

I only need those which produce the fault condition.

That's correct, although mine sames TIMED and ONCE.

The problem does only occur when the programmer is set to ON. As far as I can tell.

Oh ok, so that was perfectly normal.

Ok, boiler is on, will try all the combo's and see what happens. Might take a while.

Really appreciate the help.

 

[Fordy81]

Ok, I might have managed to fix it.

I bought a new room thermostat, just in case. And it is switching off the boiler. Have tried it quite a few times and seems to be ok. The light on the boiler that flashes when requesting heat before it fires up, goes off.

Just going to wait for it to get back up to temp, open all the windows and doors, and see if it fires up again.

The only thing was I requested 23, and it switched off at 22.5 (little flame on the thermostat went out). Is this normal/ok?