Request to heat one radiator is not firing up the boiler, any ideas why?

Phil87

Hi,

I recently installed 2x Tado wired thermostats to replace existing wired thermostats as the heating is split into two zones - 1x upstairs and 1x downstairs.

I have also installed the smart TRV's on all radiators, except for the living room which was the radiator selected to permanently leave on.

Yesterday, I noticed that requesting heat to a single radiator upstairs did not fire up the boiler; although it did show some activity on the display of the boiler, including the boilers current temperature and occasionally a no water flow error code. There was no flame icon to indicate the boiler was heating.

On requesting heat to a second radiator, anywhere in the house, the boiler would fire up and work as expected.

This issue only happens when requesting heat to a radiator upstairs. Requesting heat to a radiator downstairs appears to present no issues, I think this is because the radiator without the TRV is automatically acting as the second radiator required to fire up the boiler.

I have also worked out that if the hot water is turned on, a single radiator will turn on so there is no need to request heat to a second radiator.

Any ideas on what might be causing this problem would be appreciated.

Thanks.

RoryFire

Perhaps with just that one rad open there isn't enough water flow through the boiler, hence the "no water flow" error code?

Phil87

Think we have found the solution.
The pump associated with the heating system has three settings - low, medium and high. It was set to low but have changed it to medium. Since then, calling for heat to a single radiator is now firing the boiler.
Thanks everyone for their help.

gary333

Is this just one specific radiator? Have you checked if the TRV has been set to "No Zone Controller" / "Independent". If it is you need to change to the upstairs controller.

Having the radiators warm up when hot water is on is very strange. Heating system should be blocked off whilst that is happening. I have noticed my boiler does appear to use the heating circuit to cool down though once hot water has been used, however Tado doesn't know about this so it would only heat up the radiators very slightly without TRV's on.

Phil87

It appears to be all radiators upstairs and yes, all are assigned to the upstairs controller.

The radiators are not heating up without a request. If I request heat to one radiator, the boiler will not fire up until I have requested heat to a second radiator.

I believe having the hot water on overcomes the issue because the boiler is firing whilst heating the water.

gary333

Is the heating request (you are asking for) on an individual radiator more than 1.5oC above what the current temperature is?

Phil87

Hmm, I believe I requested maximum temperature (25oC), however let me double check that this morning.

I wasn't sure if the 'no water flow' error code on the boiler had any relevance. Again, this only shows when heat is requested to a single radiator in any room upstairs, with the water and all other radiators switched off.

Thanks for your help so far.

johnnyp78

Are both your wired thermostats set up as zone controllers and are the rooms correctly assigned to them? I’m assuming if you’ve got smart trvs you’ve created individual rooms for them on the app rather than just upstairs/ downstairs zones.

Phil87

Yes, all TRV's are registered as separate rooms and I have assigned them to the appropriate Zone Controller.

Just to confirm, I did a repeat test this morning.

I turned on 1x upstairs TRV requesting 25oC. All other TRVs and the hot water were switched off at the time. The boiler did not fire up but the display unit on the boiler lights up displaying the current boiler temperature suggesting it knows there is a request, it just isn't firing up.

Downstairs (Zone 1) is different, i can call heat to an individual radiator and it will heat up. Bear in mine, one radiator downstairs doesn't have a TRV so it is effectively the same as requesting heat to 2x radiators when I turn a TRV on. The radiator without the TRV is in the same room as the downstairs thermostat. I can heat that radiator on its own using the thermostat which again suggests the issue is upstairs only.

Do I need to remove a TRV upstairs maybe, like the set up downstairs, due to it being a separate zone?

johnnyp78

I don’t see why you would need to unless there’s a prsssure lock out, which I don’t think is what’s happening. You could also check the zone valves to see if the upstairs one is sticking.

If you’re referring to the advice not to have a trv and thermostat in the same room, that doesn’t apply to Tado devices because only one will be the measuring device so there’s no conflict.

Phil87

Thanks for the feedback.

As I mentioned, when I request heat to 1x radiator, the boiler starts up and displays its current temperature but doesn't fire up.

I can feel heat in the radiator that has requested it which is around the same temperature as the figure displayed on the boiler; this makes me think it may not be a valve issue. Obviously the temperature gradually decreases with no flame.

It appears that the boiler is doing everything it is supposed to, except ignite when a single radiator upstairs requests heat.

Switching two or more radiators on, or requesting heat to 1x radiator whilst the hot water is on and everything works fine..

The idea behind removing a TRV would ensure 1x radiator is always 'on', so when I request heat to my 1x preference radiator, there are effectively 2x radiators calling for heat and no ignition issue.

johnnyp78

I can’t see how it wouldn’t be a valve issue. I’m assuming no Tado product is connected to the boiler, only to the two zone valves? Is it a combi or system boiler?

Might be time to call in a professional or if you can do, short the upstairs zone valve so it’s open and try connecting a Tado device directly to the boiler to see if it will make it ignite.

Phil87

Thanks for the advice.

I have an Ideal Logic Heat H15 Regular Gas Boiler and a Evocyl water cylinder and the 2x Tado thermostats replaced the existing thermostats.

Are you thinking the valve could be sticking or would this be more of a set up/wiring issue?

Tado professionals advised me to increase temperature flow on the boiler this morning which I did to no avail.

I will reach out to a professional and feedback when I find out what the issue is.

johnnyp78

It could either be a stuck valve or a wiring issue, best to see what a professional says.

Phil87

So as a test, I switched back to my original thermostat and TRV’s upstairs (Zone 2) and turned up the heating with only 1x TRV open; this presented the exact same issue i.e. the boiler didn’t fire up but did light up with its current water flow temperature and a intermittent ‘no water flow’ error code again as the temperature reduced. On opening a second TRV, the boiler fired up but kept cycling, reaching 70ish and turning off, dropping down to 40ish and firing up again.
If the issue does relate to low water flow through the boiler, are there any suggestions how I can resolve this?