Intermediate · Unit 1 · Written and being checked
Reading branded units
In short
The makers' own terminal maps: a programmer in two halves wired by its printed screws, mains-switched against volt-free, the installer's link, the cylinder stats' numbering, a branded valve's own lead, a boiler's and a combi's own strips. Most units are based on a maker's, some are DrawWarm's own, and every output is proved. This unit is written and being checked; it opens to learners when it is ready.
In this unit
A maker's terminal map
A programmer based on the Honeywell ST9400C, in two halves: its front taken off, its back-plate read from its Manual, its hot water and heating outputs wired by their printed numbers, and each proved at the lamp it feeds.
Mains-switched or volt-free
Two dual channel programmers side by side: one based on the Drayton LP722, its switches fed from L inside; one based on the Horstmann H27XL, volt-free, its commons fed by the installer's links. Each is read, wired and proved.
The installer's link
Two timeswitches on the same kind of universal plate, based on the Danfoss TS715Si and the ESi ES1247B. The last engineer wired one of them from habit: read both maps, find the mistake, isolate, put it right and prove it.
Cylinder stats: read the label
Three cylinder thermostats, one job: one based on the Honeywell L641A, one on the Drayton HTS3, and DrawWarm's own dual stat, numbered the other way. Each call is wired to a lamp by its own number and proved cool and hot; the HTS3's satisfied screw goes on a fourth lamp, its cover back on before the power.
Branded valves: the same five cores
Three pre-wired 2-port valves, based on the Honeywell V4043H (five-core and six-core) and the Drayton ZA5/679-2. Their leads are read in the Manuals, and the six-core's cores landed on a Compact Wiring Centre. Open, its grey reaches the orange; shut, a heating call on its white reaches the orange.
A boiler's own terminal strip
A heat-only boiler based on the Worcester Greenstar 27Ri / 30Ri: its terminal box opened and its strip read against the Manual, the pump wired on the boiler's own pump screws, the controls fed from 230 V OUT and their switched live brought to LR, both boxes shut before the power, then fired and proved.
A combi's own strip
The DrawWarm Combi with its two factory links: the heating link taken out for a room thermostat, the hot water link left in, the thermostat fed from 230 V OUT and its call brought to LR (HTG). The heating fires on the thermostat, and the tap runs hot.
In the simulator, you practise how to
- Read a branded unit's Manual and its printed screws before wiring it
- Tell a mains-switched programmer from a volt-free one, and where a volt-free common's live comes from
- Fit, or take out, the installer's link, and prove what it changes
- Read a cylinder stat's call and satisfied screws from its own label, whichever numbers it prints
- Land a branded valve's own lead core by core, the six-core's white included
- Open a boiler's or a combi's terminal box, read its strip against the Manual and wire its demand and its pump
Checks and credit
- A timed check at the end of the unit, its questions drawn at random. The score goes on your record.
Certificates of completion and credentials are DrawWarm’s own. They record practice and tests in the simulator. They are not a formal (regulated) qualification, and they do not show that anyone is competent to work on a heating system.
Units based on makers’ products
The units in these lessons are the simulator’s own, simplified for teaching. Each is based on a maker’s product and may differ from it: on site, read the unit’s own instructions.
- Based on the Honeywell ST9400C
- Based on the Drayton LP722
- Based on the Secure / Horstmann H27XL
- Based on the Danfoss TS715Si
- Based on the ESi ES1247B
- Based on the Honeywell L641A
- Based on the Drayton HTS3
- Based on the Honeywell V4043H (6-core)
- Based on the Honeywell V4043H (5-core)
- Based on the Drayton ZA5/679-2
- Based on the Worcester Greenstar 27/30Ri
Makers’ names and model numbers are trade marks of their owners, used only to say which product a unit is based on. DrawWarm is not affiliated with, or endorsed by, any maker named on this site.
Where it connects
Read the explanation
- How to read the wiring diagram on the back of a programmer or thermostat
The terminal map on a programmer or thermostat: L and N, the numbered outputs, COM, NO and NC, mains-switched against volt-free, and the installer’s link.
Practise it in the simulator.
Runs in the browser on a laptop or desktop. Cancel any time.