Issue with boiler constantly running even when heating is off

adamk13

I have replaced old Potterton EP2002 programmer with a tado kit (Tado V3+ Wireless Heating & Hot Water Smart Thermostat). I followed instructions to the letter and all seemed to work OK… until I noticed that the boiler is constantly running even when the heating stops (ie. both lights for heating and hot water are off). I think it keeps heating the water cause I can hear some noises from the cylinder).

Any idea what might be causing this issue?

Photos of old wiring and tado wiring attached.

policywonk

According to this picture from an EP2002, these were the Pin arrangements as they would apply to a Tado extension kit:

PIN 1. HW NORMALLY CLOSED (NC) - ie OFF - in your case, nothing was wired in originally.

PIN 2. CH NORMALLY CLOSED (NC) ie OFF - in your case, was wired in originally on the pale blue wire

PIN 3. HW NORMALLY OPEN, ie goes live, or ON when there is a call for Hot Water, had the brown wire in the cable that is shared with PIN 2

PIN 4. CH NORMALLY OPEN. ie goes live, or ON, when there is a call for Central Heating, had the Green/Yellow wire connected.

PIN 5. COMMON FOR CENTRAL HEATING was originally connected to the other cable's brown wire, via an intermediate RED wire.

Theoretically this doesnt seem to be a problem, however something is unusual: Central Heating is being switched OFF when there ISNT a call for heat, whilst HOT WATER is switched ON when there IS a call for heat. This is unusual and inconsistent. Most boilers are triggered by switched live when there is a call for heat, it seems your boiler has been arranged to be permanently on for central heating, and switched off when the thermostat says so.

Did you instal a wired Tado thermostat when you installed this extension kit? If so, I strongly recommend that you have your wiring centre and the wiring arrangements to the boiler set up reviewed carefully so that

1. When there is a call for heat for Central Heating, the pin market NC is not wired, and the pin marked NO is wired.
2. Whatever provides the connection to the CH NC and CH NO is rewired to ensure this is the case.
3. The wiring centre in your home, which probably drives some motorised valves have their signals rearranged to reflect this approach.

This does not mean one can just switch the cables. There has been something strange in the wiring which needs to be addressed by someone who understands the logic of S Plans and Y plan wiring.

Now this is only my opinion. There is someone more experienced on this forum.

@wateroakley - your thoughts? Need another pair of eyes on this. Have I misread the pins?

wateroakley

Hello @adamk13 Welcome. @policywonk The EP2002 wiring to Tado looks to be correct*. Other suspicions would be (a) the wireless receiver settings for Pumped/Gravity?, or (b) a zone valve fault?

Questions and things to look at.

1. * It's often necessary to decipher the original wiring centre as well. A picture would help.
   
2. What is the make/model of boiler?
3. Is the boiler/heating: (i) Fully pumped? S-plan or Y-plan? Or (ii) Gravity HW and pumped CH?
4. The old programmer base suggests there is slot to turn and select 3. (i) or (ii)?
5. The answer to 3. matters for setting the Tado wireless receiver mode: fully pumped (default), gravity, or combi.
6. Modern boilers usually have a pump over-run, so it can be running after the zone valves or controls say 'OFF'.
   
7. If the boiler is always ON, the next check is what the zone valves are doing. Zone valves can fail any time from new to 20 years. Sticking or siezed 'ON' is very common.
8. Two-way valve check: there is a spring-loaded lever to set the manual mode. Is the lever hard to press against (to the right) with your thumb? That suggests it's OFF. Or is it easy the move? Which suggests it's ON - from the controller telling it to move to ON, or siezed ON.
9. Three-way (mid-position) valve check: No easy way to figure out what they are doing. Faulty three-way valves can do all sorts of wierd things. Mis-wiring can also do wierd things.

With more information for 1-8, that would help us to help you.

Safety note: please add some brown sleeving over the green/yellow wire on CH NO to denote that it is LIVE. If you dont have sleeving, BROWN (or RED) insulation tape would help.

adamk13

@policywonk @wateroakley - thank you for your responses, much appreciated.

1&2 - pictures attached

3. it is (ii)

4. it was set to gravity (ii)

5. Tado is set to gravity (blue light).

6. Yes, but on one occasion the boiler was running all night (so about 7 hours) - so I guess too long for overrun.

7&8 - the valves seem to be working OK when I switch back to the old programmer so assuming they are not faulty.

Now, I've noticed another strange behaviour - if I turn the heating on it does happen now and again that the boiler turns on but is not pumping hot water into radiators. I am still trying to understand the patterns but it seems to happen more if I want only a small increase in the temperature (like maybe a 1 or 2 degrees).

In addition (after reading half of this forum) I've tried tapping with the back of the screwdriver on the wireless receiver and that seems to help (as I said I am still watching its behaviour) which would suggest that perhaps the device is faulty (?).

Kind regards,

adamk13

policywonk

There seems to be a motorised valve involved which is developing a fault. Normally the decision to turn on the pump and fire the boiler is part of a sequence, where:

• The programmer allows heat to occur. EP2002s are excellent when they work, but their on-off slide tracks do wear out and throw faults after 7-8 years
• When the programmer authorises time to register heat requests, the thermostats confirm where it is needed and passes on the request.
• The zone valve(s) receive that and open their ports to meet the demand, electrically also confirming that it has happened.
• The pump and the boiler receive the confirmation from the zone valve, which then supplies power for them to start. If one or both doesnt fire, there could be a problem with the zone valve.

Do you have the time, a multimeter and expertise to check for the fault, or you open to hiring an electrician? Seems like a worthwhile next step.

wateroakley

@adamk13 If 'tapping' on the wireless receiver, turns ON or OFF, I'm minded to suspect a faulty receiver. Zooming in on the picture - can you check that the CH wires are seated correctly? The other descriptions point to a zone valve fault. Always possible that you're trying to figure out what is going on with two faults that will interact.

As @policywonk suggests, the best way of figuring out what is going on at the receiver is with a multimeter and/or voltage detector.