HONEYWELL ST9400C Thermostat Programmer. 7, 2-Channel, 3 on/Off per Day, 24 V, White, 1

Product Information

A programmable thermostat for a combi boiler need only control the heating, as the hot water is instantaneous. The table below shows a selection of standard and smart programmable thermostats from Honeywell, Baxi, Ideal, Nest, Tado and Drayon. This is called a ‘single channel’ programmer. The single channel (as in radio channel) is for the thermostat to send a signal to the boiler. NB these are compatible with heat only and system boilers however a separate control for hot water will be required. Under the new Boiler Plus regulations a new combi boiler must be fitted with an ‘advanced heating control’ (see below). wireless thermostats with programmers (non smart control) All Honeywell ST9400 models incorporate the Line of Text (LoT™) display that gives clear plain English instructions whenever any button or slider is used. This means that installers, customers and users can operate all of the controls reliably, without needing to find an instruction manual. If you wish to control your heating and hot water from a single control you will need a programmable room thermostat with two channels: one to signal to the boiler to come on and one to control the hot water. It is common to have a two-channel programmer and separate thermostat, although we have only considered combined heating and hot water units below. We review a mix of standard and smart programmable thermostats from Honeywell, Myson, Worcester, Vaillant, Nest and Tado. For more programmable thermostats try our Guide to Wireless Programmable Thermostats. wireless thermostats for heating and hot water

Weather compensation works in the same way but uses the external temperature. This traditionally involved a temperature sensor on the outside of a property linked to the internal programmer/thermostat. The sensor is able to forewarn the boiler of a change in outside air temperature which will eventually lead to a decrease or increase of inside temperature.Every boiler installation must have an ErP efficiency of at least 92% (see our Guide to Boiler Efficiencies). The common aim of all advanced controls is to ensure the boiler is on for the shortest possible time to meet the room temperature. Standard controls tend to overshoot the room temperature by 1 or 2 degrees which is very inefficient. Advanced controls reduce the heat output of the boiler as it approaches the desired temperature to prevent overshooting. The net result is a reduction is gas use and lower fuel bills.

TOP TIP make sure your advanced heating control is compatible with your preferred boiler. If the advanced control uses weather compensation, load compensation or both then the control and the boiler must be able to communicate with each other in the same ‘language’. Most boiler manufacturers use a bespoke language that means only their ‘compensation’ controls can work with their boilers. Some boiler and control manufacturers have adopted the ‘Opentherm’ language which means that differ products, such as a Honeywell control and Baxi boiler can speak with each other. See our Guide to Opentherm products and alternative controls 4) Which control do I need to comply with Boiler Plus? require the same time and temperature control but with an additional ‘advanced’ energy saving feature, i.e weather compensation, load compensation or smart controls that combine automation and optimisation features. (Or a flue gas recovery unit) New installations of a combi boiler:Slightly different minimum requirements apply depending on boiler type (combi, heat only or system) and whether the heating control is being fitted to an existing installation or fitted as part of a new boiler. The boxes below set the requirements according to your circumstances. Remember to fit a compatible Boiler Plus product. If you are fitting a new boiler with a smart heating control we strongly recommend you review our Guide to the Best Smart Controls or Guide to Opentherm products and alternative controls for non-smart products. New installations of a heat only or system boiler: Traditional programmable room stats turn the boiler on and off, for example if you only want your boiler to come on in the mornings and before you get home from work as well as set the room temperature. A standard central heating programmer (or programmable thermostat) will allow you to set the boiler to come on at the same times each day, for example, from 6am – 8am and 5pm until 9pm. Setting times for central heating and hot water to switch on and off can help reduce your home's energy consumption. Some weather compensation systems use data from the local weather station to inform your heating system of a change in temperature. This is less accurate but makes for a more straightforward installation with fewer parts to go wrong. These work with regular and system boilers to control two separate heating circuits plus the hot water. These are only used in larger properties where the ground and first floors are separately piped to create two radiator circuits (called zones) or where there is a mix of radiators and underfloor heating. Load and weather Compensation

Review and compare Smart Controls, including Boiler Branded smart controls, also referred to as remote heating controls, internet controls and wifi controls. Load compensation takes the difference between the lower internal room temperature and the desired room temperature and adjusts the boiler’s output to close the gap as efficiently as possible. For both weather and load compensation controls, the boiler can respond by increasing or reducing its output slowly to meet the predicted change in temperature. This leads to less ‘cycling’ (the boiler coming on and off) and more efficient periods of operation. NB for a control of this type to work it must speak the same ‘language’ as the boiler - for more go to our Guide to Advanced Heating Controls or try our Guide to Opentherm products and compatibility. Smart controls with automation and optimisation functions An additional energy saving measure must also be installed for combination boilers from the following list (a-c are all advanced heating controls):

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Measures A and B are forms of advanced heating control designed to work with modern ‘modulating’ boilers, i.e. they can adjust the output of the boiler to meet a varying demand. For example they can lower the output during spring and autumn months and increase it during winter. Measure C uses AI to learn your heating patterns. Optimisation technology learns when to bring the boiler to meet your desired room temperature in the most efficient way ( for more see our Guide to Advanced Heating Controls). If you want to set different times on different days, you will need what is called a ‘seven-day’ programmable thermostat. Combi, heat only and system boilers are compatible with programmable thermostats but you will need to factor in hot water controls if you have a heat only or system boiler. This is a very simple system and can mean the boiler comes on an off all day to meet the room temperature unless you manually turn the temperature down. It also means that the boiler tends to ‘overshoot’ the set room temperature by 1 or 2 degrees.

For smaller properties, the work and cost involved in re-piping the system to create two zones is rarely worth it. There are more cost effective, and less disruptive, ways of achieving variations in temperature. At their most basic, heating controls tell the boiler to come on and go off via a room thermostat. A room thermostat is set to the desired temperature and it will tell the boiler to come on until that room temperature is reached. Once reached, the thermostat will tell the boiler to go off again. These take the form of a digital display or a dial thermostat. The Honeywell ST9400C Two Channel unit is a 7 day full programmer that gives great flexibility offering up to three on/off switchings per day, additionally each day can be programmed differently, which is ideal for when the user has different heating needs from day to day. The Honeywell ST9400C can be set to 5/2 day or 1 day programme during installation. The conventional way is to fit Thermostat Radiator Valves (TRVs). This will allow you to control the temperature of each radiator, e.g. turning off radiators in little used rooms and turning them down in the bedrooms. This is a manual exercise but once done rarely needs changing. TRVs can be fitted to most radiators by a plumber. For a comprehensive review of 32 TRVs regard our Guide to Thermostatic Radiator Valves. Smart Radiator ValvesIf you are extending your property significantly, you may wish to consider separating the ground and first floor radiators in this way. It will involve re-plumbing parts of the system and additional pipework, as well as adding zone valves to each circuit. Thermostatic Radiator Valves