CH flowing cold (without call for heat) - Tado / WR1

[SuperSix6]

Afternoon All,

Moved home recently and installed Tado V3 to replace EMP2 timer and a WR1 / thermostat.

HW worked okay but CH didn't until I realised the WR1 receiver next to the tank was still controlling the call for heat, so from searching I've joined terminals 1+3 together in the WR1 and Tado now controls CH and boiler fires as expected when heat is called for.

However I can now hear and feel cold water flowing through rads 24/7.

I wanted to check if this is normal? Having only been here less than two weeks I am certain before joining 1+3 on the WR1 I could not hear cold flow through the rads and wonder if perhaps at the time 1 + 3 were joined (prior to switching power off) a valve has been left permanently open?

I have some basic plumbing experience, have worked on my partners combi system before and my previous property was a new build with sealed system which I never needed to touch.

This is an old Edwardian property with presumably a vented system.

Thanks

 

[stem]

It sounds like you may have an old heating system where the CH setting controls the Pump and the HW the boiler.

As the system originally was, when you turned the CH on at the EMP2 timer did the HW come on with it as well?

Can you provide details of the heating system does it have motorised valves and a hot water cylinder thermostat for example.

How have you wired the Tado in?

 

[SuperSix6]

It sounds like you may have an old heating system where the CH setting controls the Pump and the HW the boiler.

As the system originally was, when you turned the CH on at the EMP2 timer did the HW come on with it as well?

Can you provide details of the heating system does it have motorised valves and a hot water cylinder thermostat for example.

How have you wired the Tado in?

I’m unsure but the original controller had separate CH and HW ‘once/twice/off’ sliders.

Do these images help identify the type of system I have?

I haven’t modified any wiring in the airing cupboard, only on the controller for the new receiver.

Thank you.

 

[stem]

Thanks for the pictures, very helpful. It appears to have a 3-port motorised valve, so all good there. In which case it's most likely to be what is known as a Y-Plan with a mid position valve. However, I can't read what's printed on its head to be 100% sure. I suspect that it's a Drayton 27101SX / MA1

The Tado should have replaced the original programmer, so the wires that went to the old programmer should now go to the Tado receiver instead. The wires in your Tado Receiver are pretty much what I would expect to see, except that with a mid position valve, there should also be a wire in the HW NC terminal as below, which appears to be missing in your photo.

 

[SuperSix6]

Thank you!

Here’s how the original controller was wired, I’m wondering if the HW NC wire you mention is actually somewhere in the receiver in the airing cupboard by the tank / WR1.

For the time being I have reinstated terminals 1 & 3 in the WR1 and left the old wired thermostat set to 30 degrees / permanently calling for heat. This has stopped the pump being permanently on.

I’ve yet to test the CH however this worked before, with the pump activating and boiler firing when the Tado calls for CH heat.

 

[stem]

There doesn't appear to be a wire originally in terminal 1 of the original programmer [HW Off] so there's a mystery.

Can you confirm that the valve is a 3-port (3 pipe connections) and not a 2-port (2 pipe connections)? 2-port valves don't need the HW off connection, but with 2-port valves I would expect there to be at least two of them.

Bridging 1 & 3 at the WR1 would normally be the right thing to do and would take the old wireless thermostat out of service allowing the Tado to take over full control of both time and temperature functions.

However, WR1 is designed to work with a wireless [RF] thermostat, but you also mention a wired thermostat!! If the Drayton RF thermostat with WR1 was supposed to have replaced the wired thermostat in the past, the wired thermostat should have been removed, or at least its switching terminals linked [as you have done at the WR1]

This all seems a bit ad-hoc. Might be time to re-wire it all up again from scratch.

 

[SuperSix6]

It looks like there are 2 x 2 port.

Sorry, I should have said wireless (not wired!) thermostat!

Strangely now this morning the pump for CH seems to be running, with the display showing ‘45’. Yesterday evening having returned wiring on the WR1 to its original state it was not.

When using Tado to call for heat I can hear the actuators moving and valve clicking, the airing cupboard then becomes much more quiet!

My HW schedule is for an hour between 7-8AM.

 

[stem]

That makes sense, so you don't need the extra wire then. And the link between WR1 terminals 1 & 3 is correct. Inside the WR1 is a switch that when the room thermostat calls for heat, terminals 1 and 3 are linked together electronically inside the unit. The external wire link just copies what happens inside the unit, so the WR1 being a problem is most likely a red herring.

It sounds to me like you may have a faulty motorised valve. Inside each valve is a microswitch that controls the boiler and pump. The external controls (Tado et al) will simply open and close the two motorised valves (one for HW, and one for CH) as required. Then the small switches inside are operated by the valve when it winds to its fully open position. This is the 'click' you hear. Over time these switches can become intermittent and can stick in the 'on' position even when the valve has closed. Sometimes they work, sometimes they don't. I suspect this is what is happening in your case. The switch is sometimes sticking in the 'on' position and the pump is continuing to run, but because the valve has closed, hot water from the boiler won't be going anywhere. So the boiler will heat up and shut down.

 

[SuperSix6]

Even the old controls see the pump running permanently, I'll get someone out to look at the motorised valve.

Unusually after restoring power to the boiler an F22 fault (Dry / Low Water) appeared which looks to have been resolved with a reset of power again.

 

[SuperSix6]

To update this, a local plumber diagnosed a wiring fault. Both 2 port valves are fine.

Must have been historic or at some point something somewhere has been changed creating a permanent live to the pump.

Easiest to re-wire than to try to trace and reverse engineer.

 

[SuperSix6]

The saga continues. I've concluded that this wiring fault was intentional to stop the boiler dry faulting, we have a mix of F22 Dry, F11 and rarely F25 Diff.

It now needs a regular reset but otherwise runs completely fine. There is still audible air in the flow and return after no demand for a few hours despite having installed automatic air vents past the pump on both the CH and HW circuits - I hear these venting small amounts of air occasionally.

My next step is to try filling the system from the drain cock so as to push any air up and out but I don't think this is really the problem.

What is unusual is that this boiler between every 10-30 minutes will fire for around 20-30 seconds without there being any call for heat or hot water, I think this is short cycling?

It may be this expansion and cooling of the water in the flow that is creating trapped air (below the pump that now isn't running) that is eventually causing the dry fault (F22). The boiler is on the ground floor and the tank and CH pump in the bathroom above. Once the pump is running and I then reset the boiler it fires and runs without issue.

I haven't yet checked if the F&E is drawing any air in but I'm confident that if the remedy previously was to leave the pump running permanently that this is unlikely and there may be a sensor or PCB issue with the boiler?

I will check what pump over run I have currently, I don't think there is any, my plumbers suggestion is that it's not sufficient to to dissipate heat when demand ends and an overrun might solve the issue.

Any ideas? @stem