Replacing a Manual Timer Switch With Modern Digital Programmer Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[salem123]

Hi,

I want to replace a defective manual timer switch which controls my boiler - its external to the boiler - with a modern digital programmer. I only want to control the central heating. At the same time I wish to move the only room thermostat in the house from the lounge to a position in the middle of the house. We have a log burner in the lounge which effectively renders the thermostat useless resulting in the rest of the house being more like a fridge.

I am thinking that a simple RF thermostat and programmer would work but was seeking confirmation that I am on the right track, ie would the new programmer be a straight swap with the old timer? Or is this too simplistic, I didn't want to get involved in touching the boiler if I could help it.

Thanks

[collectors]

How is your hot water heated? Is it not via the boiler.

[salem123]

Hi, yes it is via the boiler but not controlled by the timer, that only controls the heating. Reading my post again I should probably have referred to the timer as being mechanical rather than manual - its the type you have to pull out pins to set on/off times

[ericmark]

Timers are often called programmers, and there are two types of thermostats, simple off/on and modulating, I expect you are using simple off/on? The normal way is to fit the off/on thermostat in a room kept cool, so when summer arrives it will switch off the heating at say 18 deg C rather than 20 deg C used in say a living room. The room as you have worked out has to have no alternative heating or outside door and on ground floor, as heat rises. It is not designed to control the temperature of the house, the TRV heads do that, it is just there to turn off boiler when summer arrives, so wants to have no anti-hysteresis software.

With hard wired thermostats this is not a problem, any old thermostat will do, but with wireless the cheap thermostats with no anti hysteresis software also have no fail save, so if the battery fails it may continue heating.

So although the thermostat with anti hysteresis is not ideal, we often have to use them.

However in your case turn the thermostat up to max, and control rooms using the TRV heads until warm enough so not using the solid fuel fire, as the thermostat is only there to turn off system in summer, it is not intended to control the room temperature unless using a modulating thermostat, if you are using a modulating thermostat then only way to use wireless is with OpenTherm and it depends if your boiler is OpenTherm enabled.

Thermostats like Nest gen 3 can work with a wifi connected thermostat to the boilers bus, but thermostats like Wave have to be hard wired, so much depends on what boiler and control you already have.

It is so easy to jump in and give advice and not consider it may have a modulating thermostat, however they are not really that common.

[salem123]

Thank you very much for your response. I quite like the sound of that. We only moved into the house in August and fitting TRV's is on the things to do list. The house is a early to mid 80's and doesn't have any fitted currently.

I am not sure if the current thermostat (Tower STT RSA) is of the modulating variety and suspect it isn't given how old it looks. I do know that it seems to be fairly inaccurate, ie we have it set to 15 degrees which is more than comfortable if the log burner is unlit. Perhaps I should just consider updating for something like for like together with the TRV's of course.

I still need to change the timer as the switch between timed/on all the time won't stay put unless sellotaped in position. Again maybe a more modern like for like solution?

Thanks again for the advice which looks like saving me some money.