Can I get rid of my Honeywell heating and water timer altogether?

23 Jan 2012
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United Kingdom
Hi there.

Am just contemplating something and would be grateful for any pointers.

Ultimately, I have a Y plan heating system that uses a timer to turn on the water whenever needed. The heating is set to continuous as we use an intelligent Honeywell thermostat for all our heating timers. I say intelligent, rather than smart, as the thermostat does not connect to the internet but does claim to turn on the hearing earlier, when it senses that the temperature starts to get colder - though it does get caught it, when the weather is suddenly different.

The main issue we have is the hot water - not only do people suddenly want impromptu baths but sometimes, for some reason, there just is not enough hot water for some reason and we have to have it run for another hour. Not only is this a bit inconvenient (given that the button is hidden away in a difficult to access cupboard) but not that flexible as you cannot schedule a bath when you are out of the house or you cannot run it for, say, just an extra 30 mins.

Would it work to just remove the programmer together and do the following:

1. Connect the live to the hearing on (channel 4 wire) with a physical switch - rather than have the timer running continuously, I could just turn the hearing off in the summer and on when it starts to get cold.

2. Connect the live to either the hot water on or hot water off (channels 1 and 3) via a Zigbee relay and then control if from my HomeAssistant server instead?
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I don't understand why you run out of DHW? With my C Plan yes, I have no cistern thermostat, so nothing to tell the boiler to fire up, but with the Y Plan the cistern thermostat is connected direct to the boiler so it should auto fire up once water cools down.

Only way I can see running out of water is if using the Willis system, where it uses time running to determine how much of the tank is heated.

If the cistern is too small, it hardly matters what you do, you will still run out of DHW when running a bath, in hard water areas the cistern can fill up with lime, so it no longer has the capacity, but no software tweak will help.

So only way to run out of DHW unless cistern is too small is to turn off DHW, or have the thermostat too high on the tank. So what is the problem?
What colour is your hot-water cylinder?

And what size?

Please show us a photo of the programmer that controls your HW times.
Pics of programmer and hot water cylinder attached (it is yellow, underneath, and about three foot in height).

It is really difficult to put my finger on what the issue is - there must be a pattern as to when the water is hot enough and when it is not but we just cannot figure it out.

A few ideas:

1. If it is colder in the house, to begin with, the timer might not be sufficient to bring the tank up to temperature.
2. If someone has not had a bath in the evening, there might be enough residual heat to mean that the tank gets up to temperature more quickly the next morning.


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A yellow cylinder is quite old, maybe 30 years.

The insulation is not up to modern standards, but yours has a red jacket as well, so reasonable.

The other difference is that the heat exchanger coil inside is smaller, so it takes longer to heat up. A modern boiler can heat a modern cylinder in about half an hour, yours, I don't know. Maybe an hour?

A 36" high cylinder is often 24" diameter and holds about 100 litres, which is about a bathful. A sink or two can use up enough that it will be short of a bath.

I have a cylinder, and set the timer to come on before the CH, so the cylinder will be fully hot before anyone wants a bath or xhower, and to continue long enough that it will be reheated afterwards for other household needs. If your cylinder is heated by gas, the cost is so low that it is not much expense go keep it hot all day, but wastage will be less if you run the boiler a couple of times a day, rather than for a few minutes every time someone runs a tap.

Modern practice is to have much larger cylinders that may hold enough hot water to last all day.
Do you have anything like this, Willis-immersion.jpg the Willis system does work on time, but that is the odd one out, nearly every other system uses a thermostat at a set level on the tank and it heats up water until the thermostat is triggered.

With my central heating boiler I have no tank thermostat, it works on the C Plan and to stop the boiler cycling all day in the summer, we set a run time, so switches on three times a week for ½ hour at a time, well actually after 20 minutes the return water temperature normally turns off the boiler. And with less insulation than you have, water stays hot when not used for more than 2 days.

So if you have a tank thermostat, can't really see any point having a timer on DHW, only reason to have a timer would be if you have different tariffs through the day.

As to central heating, I must agree with you, can't really understand why we have a programmer or wall thermostat, it does seem some thing left over from a by-gone age.

I have a thermostat in every room, built into the radiators, called a TRV (thermostatic radiator valve) some are blue tooth (5) and some are connected to internet (4) and the latter gives me a report
Flat Battery TRV.jpg
so if the target is above current with any TRV I want the central heating to run, I have a wall thermostat but no link between the two thermostat types, so it needs carefully setting the TRV and wall thermostat so boiler is turned on when required.

EvoHome seems to allow you to adjust the TRV's from a central point,
but all the others seem to be a bit of a Heath Robinson set up. Yes I can look at my PC Heating not keeping up.jpg and it shows the 4 TRV's and the wall thermostat, but they don't talk to each other. And the charts Energy History Nest.jpg are really a waste of space, it shows when the wall thermostat was allowing the boiler to run, not when the boiler was running, and depending on how many TRV's are open the boiler will be cycling on/off over that time, so not a clue how much oil I am using.

But my TRV heads do have IFTTT it seems, so likely some one clever could get them to turn on the boiler, used IFTTT to work geofencing, not that it worked very well, but not to control boiler.

It seems Hive uses zigbee, and we can use voice commands, but still needs some form of Human Machine Interface (HMI) to work, I don't seem to be able to say hey google get living room to 20ºC I get answer I don't know how to do that yet, go to Google Home app.

It seems all the bits are there, it just does not interconnect. I use oil so not as flexible as gas, but in theory with gas all one needs is an on/off switch to turn it off in summer, and the TRV's should work with boiler to get each room at the programmed temperature without any wall programmers or thermostats.

But like you, it seems we don't have the software to connect up all the bits.

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