Boilder and pump keep running when demand has stopped

[ice123]

Hi all, hopefully someone can offer some advice:

I have a potterton profile 80 boilder (I know quite old!). It's a S-PLAN system. Over the last few months, the boiler control has been a little eractic, but I have struggled to nail it down. Lately, it's now been running all the time (pump permanently and boiler as and when the boiler circuit temp drops). There is a bypass valve installed, which when the water is flowing through, makes a different noise, so it's easy to recognise.

After a little investigation, I confirmed that none of the valves were open (4 x 2 port valves in total). I wondered whether one of the micro-switches was sticky, so disconnected all of the outputs from the valves that were connected to the switched live. After turning the power back on, it was still running!

My initial thoughts were a failure in the over-run pump control somewhere, but that would't explain the boiler firing would it?

Of note:

• the gravity / fully pumped switch is in the fully pumped position
• boiler thermostat control set to 2.
• Drayton MyGenie heating control system

I would be really grateful for any thoughts.

Thanks

 

[SJB060685]

And you have confirmed neither zone valve end switch is stuck by removing each orange wire from switch live to boiler?

 

[Ziggie]

From your comments , I think you disconnected all the orange wires links to the boiler and the boiler is still working? Or checked they are not live!
If no then as stated above
If yes then
thiswould seem to indicate that SL was still live from somewhere and this is firing the boiler and through it the pump.

quess (unlikely) is the live feed to the boiler connected into the SL?

or is there a relay stuck linking L and SL in boiler. (I know nothing about internal wiring of boilers)

needs gas safe man to investgate
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And just to double check the obvious.The pump will run on until the water in the boiler cools (modern systems power pump from boiler). This normally runs on for 5-10 minutes after demand stops.

if the pump runs on without the boiler, then problem lies within boiler

 

[Murdoch]

When was the MyGenie system added to the system?

 

[Gasmk1]

Is there a frost thermostat anywhere which may be faulty or set wrong

 

[ice123]

And you have confirmed neither zone valve end switch is stuck by removing each orange wire from switch live to boiler?

Exactly that. Infact, removing every orange wire, it still activates the boiler and circulation pump! strange!

Next I will try disconnecting the SWL from the boiler and if that stops it, I know there's a wiring fault somewhere in between.

It doesnt help that the various components are spread across the house!
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From your comments , I think you disconnected all the orange wires links to the boiler and the boiler is still working? Or checked they are not live!
If no then as stated above
If yes then
thiswould seem to indicate that SL was still live from somewhere and this is firing the boiler and through it the pump.

quess (unlikely) is the live feed to the boiler connected into the SL?

or is there a relay stuck linking L and SL in boiler. (I know nothing about internal wiring of boilers)

needs gas safe man to investgate
[automerge]1576613837[/automerge]
And just to double check the obvious.The pump will run on until the water in the boiler cools (modern systems power pump from boiler). This normally runs on for 5-10 minutes after demand stops.

if the pump runs on without the boiler, then problem lies within boiler

Thanks for your thoughts. Yes, having removed all orange demand wires originating from each of the 4 valves, the boiler still fires. As you say, if it was the overrun kicking in to cool down, I wouldnt expect the boiler to fire, which it does!

I have yet to disconnect the inputs to the SWL at the boiler end, which I shall do shortly. As you say, if that doesnt solve the problem, the issue must lay within the boiler.
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When was the MyGenie system added to the system?

about 2 years ago. Has been fine since then. Thanks.
[automerge]1576835237[/automerge]

Is there a frost thermostat anywhere which may be faulty or set wrong

Good thought, but I don't think so, and in any case having removed the SWL feeds, this should stop it anyway right (unless the frost protection is within the boiler which I don't think is the case).

 

[Ziggie]

I would also check that there isn’t a link into the wiring centre to the junction of the orange wires. I recall some wiring centres have built in links joining terminals. Could it be that?

The boiler may have frost protection or something else built in and the thermostat might have gone ?

The pump may have a dedicated live which is providing power to the boiler through back feed.

checking voltage at the slw with the orange disconnected should provide info

 

[SJB060685]

I cant say about gas boilers because I'm not trained or qualified but oil boilers that have a frost stat are wired in to bring in CH momentarily, if wired in correctly to today's standards. You need to eliminate the possibility of this by searching for a frost stat, although a 20 year old internally mounted gas boiler probably doesn't have one? Perhaps these gas men can confirm. Next as above the wiring centre needs to be checked for any permanent live links that may have been mistakenly installed. Does the boiler have a permanent live to it? If the answer is no then you must be getting your feed from somewhere.
Also I have come across systems with two live supplies into wiring centre from two separate switches fused spurs, needless to say I learnt the hard way with a shock.

 

[garygvl]

disconnect swl at boiler terminal. if stops problem elsewhere. if still carries on firing with pump running you need to check Gravity/Fully Pumped Selection Switch is in correct position on boiler and is operating correctly and not shorting internally which would give you the problem you describe
[automerge]1576868752[/automerge]

I cant say about gas boilers because I'm not trained or qualified but oil boilers that have a frost stat are wired in to bring in CH momentarily, if wired in correctly to today's standards. You need to eliminate the possibility of this by searching for a frost stat, although a 20 year old internally mounted gas boiler probably doesn't have one? Perhaps these gas men can confirm. Next as above the wiring centre needs to be checked for any permanent live links that may have been mistakenly installed. Does the boiler have a permanent live to it? If the answer is no then you must be getting your feed from somewhere.
Also I have come across systems with two live supplies into wiring centre from two separate switches fused spurs, needless to say I learnt the hard way with a shock.

potterton profile should have permanent live to it when on fully pumped system for pump overrun that is assuming pump is wired back to boiler as should be. wouldnt expect hidden links to suddenly appear in wiring centre after all these years

 

[SJB060685]

Thanks for info on the boiler. I agree links wont magically appear, I was simply going through all the potential causes

 

[Ziggie]

Thought that I didn’t problem solve properly - so bear with me as a non electrician and non plumber.
Definition of problem : boiler runs when there is no demand on an S plan system
Check 1: confirm that hot water is not gravity fed and central heating is S plan.
Check 2: No demand means all timers and thermostats are not requesting.

Check 3: does the 3amp fused spur switch work and stop the boiler?



question 2: when did the problem start and when can you say the system was last working properly?
Question 3: any changes at the time ?
Question 4: is problem reproducible ?

 

[Ziggie]

Hi,

given the time delay, can we assume that the problem has been fixed.

it would be very helpful if you could let us know the solution to add to the knowledge base.

 

[ice123]

Hi,

given the time delay, can we assume that the problem has been fixed.

it would be very helpful if you could let us know the solution to add to the knowledge base.

Sorry for the delay in getting back on to this forum. After extensive troubleshooting, turned out that a loose wire within the boiler was causing it to fire ??!! Having removed the erroneous wire. it seems to be behaving as it should. Nobody has touched it since it was last serviced, so no idea why this happened. Boiler being serviced soon so will ask them to make sure all is OK.

Thank you to all who helped with the diagnosis.