Boiler on, boiler off... hot water taking ages to heat

nubink

Hi,

I have been lurking here for a month or so since installing the Tado X.

Replaced a Drayton LP722 which is connected to a Glo-Warm Flexicom 15HX

There are no extra connections to the Boiler (I am aware of a wireless device that can connect)

I followed instructions as per the Tado X installation notes and wired appropriately.

It doesn't feel as if it is working correctly…

the house gets warm, but the water can take an age to heat. Sometimes we have 54deg hot water in the morning and sometimes it is 41deg.

I can hear the system click off and then back on again with in a second. It will stay on for a period of time and then click off and back on again.

Looking at the boiler, if I set the boiler max flow to 65deg for instance, I will see the boiler light up, heat up for a bit and then get switched off (by, I assume this off and on process from the Tado X). Sometimes it will fire for long enough to get to the max temp, sometimes it will only fire for a couple of seconds and then back off again.

The result of all of this is that the water is never allowed to get to max temperature to enable a relatively quick heat up of the hot water tank - the water in the tank has stayed on 41deg today for over an hour…. (I have an external thermostat a third of the way up the tank set at whatever temp I want it to be)

I have tried switching off the CH, disconnecting the HC and the HO cables, restarting and resetting…

This behaviour appears to be it's feature… sort of randomly guessing when to switch off the boiler to keep the condensing element of the boiler working

Is this right???

Wiring diagrams attached…

Thanks

Gary

policywonk

You have a boiler which can operate in dry switched (dumb) on-off mode, or in digital controlled mode. Internally the boiler controls the energy it generates and literally throttles the gas depending on the calculated heat it is required to produce minute by minute. Now that energy output is then trimmed because it measure the temperature of both outgoing and incoming flow pipes. This is not a dumb boiler and it isnt a simple process. It even uses a differential flow pump to save energy.

When you set a higher flow temperature the heating curve becomes steeper, and that instructs the boiler to be more reactive to the difference in temperature between the flow and return pipe. The higher the flow temp, the more the boiler will cycle.

Now, here's something you might want to consider.

1. Your original thermostat/programmer the LP722's installation guide is here: Invensys B/sheet_TO PRINT - basically it ran the boiler in dumb, on-off mode.
2. Your Tado X environment seems to also be set in dumb mode, not in digital mode- and am aware that the X series will only operate Opentherm digital mode, but are you aware that the V3 series can handle the E-BUS mode which more carefully marries with your boiler's capacity to throttle output and reduce waste?
3. How long has it been since you bought the X series? Were Tado made aware, in writing, of the exact model of the boiler when you asked for instructions?
4. Does your home have multiple zones with zone valves which led you to form the view that the basic on-off switching mode was best for your setting?

nubink

Thank you for the information about the boiler… that makes sense with what I am seeing.

I also think that it is time to clean out the system - I found out that there may be a possibility for the boiler to go into low flame mode if it is having issues with water movement… and it is ten years old…

On that point, the Tado was bought as a compromise for this boiler, recognising that the Tado X will work in a relatively dumb mode now, giving us some app control over room heating while using a on off process for modulating the boiler. When the boiler is finally replaced with a heat pump (albeit with an addition) we can start getting the benefits of the Tado system - which will be a change sometime this year or early next.

I was surprised, given the on-off nature of the system, that it wouldn't just switch on the boiler when hot water is requested. Tado has no idea what the water tank temp is, so I assumed that it would switch on the boiler - let it do it's thing based on the max temp that I had set on the boiler - and then go back to cycling the heating for the CH based on room temp increase.

Also, and very disappointingly, I notice that the plumber who installed this boiler all of the years ago, configured the Honeywell wiring centre as a 'S' Type system rather than the 'Y' Type system that I have. This has now been rectified (with a Drayton Wiring Centre. Much easier to determine what's going on).

policywonk

10 years old, with older plumbing. Got anybody locally, an ageing plumber who can do a reverse pressurised cleanout of your heating system? We have three boilers here at the charity. One was continually cycling and when changing a TRV, realised that the pipes were jammed with black oxide. We got hold of some volunteers, studied youtube, hired a central heating pressure cleaner. It took two days (19 radiators), but after that, things really improved - and most importantly we were using far less fuel.

Do consider replacing the X with a V3 system if you intend to keep the boiler, if you've got the time this summer. As you've already learned how to tidy up your wiring centre - which is so crucial IMHO - you may feel comfortable in moving from dumb on-off controls to E-BUS, which the V3 series handles well. I dont know why Tado decided to drop that support from the X series, but it does work.