The joy of being a Heating Engineer

Except for differing heat output these two wall mounted boilers are otherwise visually identical. For use on sealed systems only, they can be installed without any specially provided ventilation and are suitable for high rise building installation where access to the outside wall is difficult. Horizontal or vertical flue systems can be up to 10m in length. Operation is semi automatic, together with a novel control panel selected feature that allows DHW ‘preheating’ to be on or off. When this is ‘on’ the boiler functions automatically to keep the DHW circuit hot so that less time is expended in heating from cold.

GENERAL

The appliance is suspended on a separate wall-mounted plate and connected to a fixing jig complete with isolation and drain valves. A vertical piping kit is optionally available.

The chassis consists principally of an air-section box with a removable Inner casing panel’; inside this are the heat exchanger, fan, gas control, ignition module, condensing trap and expansion vessel.

All the other electro-hydraulic components are located behind a drop-down control panel hinged below the box on a lower shelf. A front panel is located on two top pegs and secured by two lower screws.

Side panels are mainly cosmetic, although if removed they will provide limited servicing access if sufficient side clearance is available. Each panel is internally lined with foam and secured by two screws on the front face.

HEAT ENGINE

Main heat exchanger

Enclosed in a largely circular stainless-steel case, the exchanger consists of five multi-coiled lengths of flat-section tubing.

The returning water first enters the two rear-most sets of coils in parallel before passing on to flow through the forward three sets. Integral manifolds at each upper side of the case transfer and pass the water between the return and flow pipes. Combustion gases from the centrally-disposed burner cool as they pass over the coils to exhaust from the casing into an ‘L’-shaped plastic flue hood that is sealed to the back of the exchanger casing.

Condensate trap

Water condensing on the coiled tubes during the heat transfer – together with any rain water and/or condensate in the flue – drains into a plastic trap fitted in the bottom of the air box. The trap featuresa float valve that excludes the necessity for filling the trap after refitment.

Fan pressure initially keeps the valve closed until the water level gradually builds up sufficiently to raise the float and thereafter allow normal syphoning action. The water exits periodically in ’slugs’ of water through a small duct within a three-quarter-inch outlet connection which also includes an air vent. The actual drain pipe is a plastic push-fit that allows for trap removal.

Gas control, fan and burner assembly

Note: This combination is always removed and refitted as a complete assembly. The Dungs gas control is a 24V DC twin-solenoid-operated control attached via three screws to the fan unit. The gas inlet pipe from the isolation valve is an ‘O’-ring-sealed push-fit into the control; the outlet port discharges through a venturi into the eye of the fan rotor. Checks/adjustments following a combustion gas analyser check are detailed in ‘Commissioning’.

Interposed between the fan and gas control mounting flanges is a plastic ’swirl’ plate featuring diffuser vanes that cause the air to accelerate and swirl before mixing with the gas and entering the fan. The variable-speed, 24V DC fan is powered by a separate ‘DC fan supply’ transformer fitted in the bottom of the air box. The transformer is complete with its own 3.15A fuse protected PCB. The centrifugal type fan rotor thoroughly mixes the gas and air and imparts sufficient pressure to carry it through the burner, heat exchanger and flue. Fan speed is dictated as a requirement of heat demand from a computation of temperature

potentiometer and thermistor measurements.

The burner occupies the full length of the combustion chamber between front and rear ceramic-fibre insulation linings and is secured by four screws to the main heat exchanger front cover.

Cleaning is restricted to dusting with a soft brush. If renewal is necessary, a new burner gasket MUST be fitted.

Ignition

The ignition module is bracketed to the main heat exchanger and wired to the main ‘control box PCB’ The electrode assembly, which is secured via a gasket to the heat exchanger face by two screws, features central and earth electrodes that also act for flame recognition with a 3.5 to 4.5mm working gap.

Expansion vessel

Mounted in the air-section box the eight-litre vessel is pre- charged to 0.5 bar. Maximum heating system capacity is 130 litres at 1 bar.

HYDRAULIC COMPONENTS

Except for those items detailed above, all hydraulically functioning components are located on or in left-hand and right-hand ‘hydroblock assemblies’ on the lower shelf of the appliance chassis. Most of the components and/or connections (or unused blanked-off ports) are sealed by ‘O’-rings and secured by plate circlips.

DHW plate heat exchanger

This is connected via four rubber seals and secured by one screw onto the back of each hydroblock. Removal involves draining both CH and DHW systems and disconnection of the primary flow pipe. The word ‘TOP’ marked on the plate indicates only one way of fitment.

Diverter valve

This is a twin-spool, spring versus motorised valve assembly located within the LH hydroblock. The valve position is dictated in accordance with demand by a 230V AC motor (called a ‘diverter switch’) on the right-hand end of the hydroblock by a plate circlip. The ’switch’ can be easily renewed without draining, but

valve spool renewal will involve system drainage and complete removal of the LH hydroblock.

Bypass valve

Located at the extreme left hand, upper rear corner of the LH hydroblock, this is an adjustable, spring-loaded valve controlling a relief line between the return and flow sides of the primary circuit. Factory setting is half a turn open. Turn clockwise to reduce the bypass. Temperature differential at maximum heat input should be 20°C.

Pressure-relief valve (PRV)

A 3 bar spring loaded system overpressure relief valve with a red cap located at the left-hand end of the LH hydroblock. To avoid the valve being used to drain the system, an operating knob is not fitted. However, to test the valve an operating tool lever is loosely secured to a nearby pipe. To use the tool (system-pressurised), remove the red cap by prising it forward and insert the tool under the valve spindle circlip. Depressing the tool lever will then open the valve. After use, refit the cap and (Glow-worm recommends) ‘locate the tool such that it is not noticeable to the customer’.

Reduced-pressure zone valve

This is fitted on the top of the LH hydroblock, to the immediate right of the PRV, and fed by the ‘fill valve’. The valve reduces mains water entering the primary circuit to an acceptable pressure that avoidsaeration. A downward facing open port will indicate any leakage.

Pump

The head of this single-speed Grundfos UP 15-60 pump is fitted directly onto the RH hydroblock. It must be removed before the wiring can be disconnected. Only the pump head is spares listed.

Return filter

Located under the boiler to the left side of the return isolation valve, this plastic filter features a flat cut-out section along its length that must be aligned correctly. Retention is by a wire clip.

DHW filter

Similar to the return filter but without the cut-out opening, this filter is located above the fill valve. Retention is by a plate circlip.

Fill valve

A screw-type shut-off valve with a blue coloured operating knob on the underside of the boiler. This controls a permanent mains feed to the reduced pressure zone valve.

Flow sensor

Fitted in the upper rear section of the RH hydroblock behind the DHW filter. This paddle-wheel-type indicator senses mains flow through the plate heat exchanger as a demand to light the burner for DHW.

Water pressure sensor

Located on the RH hydroblock to the left side of the DHW filter, this sensor monitors primary system pressure. A pressure below 0.7 bar will cause shutdown.

TEMPERATURE DEVICES

DHW thermistor

This wet thermistor is fitted on the LH hydroblock monitoring the outgoing DHW temperature.

CH flow and return thermistors

These identical sensors are spring-clipped onto their respective flow and return pipes on the left side of the main heat exchanger. Resistance at 25°C is 10 KΩ

Overheat thermostat

This manually-resettable sensor will cause shutdown in the event of a flow temperature exceeding 86°C. The sensor is spring-clipped over a specially flattened section of the flow pipe.

KEY

1 Flue gas analysis test point

2 Internal flue duct

3 Main heat exchanger

4 Burner

5 Sight glass

6 Ignition electrode

7 CH expansion vessel

8 Condensate trap

9 Gas control

10 DC fan

11 Water pressure sensor

12 DHW plate heat exchanger

13 Pump

14 DHW flow switch

15 Fill valve
16 Primary return filter

17 Primary drain valve

18 Mains inlet filter

19 Mains pressure restrictor

20 DHW outlet thermistor

21 Pressure-relief valve

22 Bypass valve

23 Reduced pressure zone valve

24 Diverter valve

25 Flow thermistor

26 Return thermistor

27 Overheat thermostat

CONTROL PANEL

This complete assembly consists of three sandwiched parts, with the central layer being hinged to the boiler lower shelf.

The front of the facia panel features two temperature control setting knobs, an LCD display window, an on/off switch and (if fitted) a timer.

This panel is slotted into the main central section and retained by snap-over latches. When opened (it should not be allowed to fall) the panel gives access to a ‘display PCB and a ‘230V controls interface’ PCB on the inner face. Clock and/or on/off switch connections are also visible.

The rear (cover) of the assembly provides a terminal block for a link or room thermostat connection. Removing the cover gives access to the ‘control box’ (main) PCB and its 125mAT fuse.

Mains reset switch

Controls mains voltage to the main PCB. This should normally be left on (position 1) to enable frost protection, pump and diverter valve exercises to function.

Control light and digital display

A fault is shown by a flashing red light and a fault code – or ‘0 bar’ if the primary system is below minimum pressure. Normal read-out shows water pressure (when there is no heat demand) – or primary temperature during a CH demand. A green control light will show whenever the burner is lit.

Fault codes

F1 = Failed ignition sequence – check fan, gas control connections, condensate blockage.

F4 = Flame loss during running – check inlet gas pressure, electrode, flue.

F9 = Sensor failure – check overheat stat, thermistor, wiring connections, faulty PCB.

Temperature control knobs

CH

• 0 = Off
• 1 = min. to max.

DHW

• 0 to white tap sector = Pre-heat inoperative. Temperature set at 62°C.
• White to red tap sector – Pre-heat operative. Min 40°C, ECO 55°C, Max 62°C.

Automatic operating features (with gas/ electricity on)

1. Pump will circulate water within the boiler only if temperature falls below 7°C.
2. If temperature falls to 3°C burner and pump will operate to raise system temperature to 10°C.
3. Pump operates for one minute and the diverter valve will cycle once per 24 hours to avoid seizure if there has been no other demand.
4. After satisfying a heating demand, an anti-cycle device will delay re-firing for 45 seconds or until a drop of 2°C is realised. This does not prevent firing for DHW.

INSTALLATION

The appliance is conventionally wall-mounted on a two-piece arrangement of a support plate and a connections jig. A Vertical’ plumbing kit is optionally available to facilitate pipe runs behind the chassis. Lift weight is 43.7kg.

Maximum flue lengths

Horizontal

10m plus one 90° bend and the terminal length (633mm) – minus any additional bend penalty. (90° = 1m; 45° bend = 0.5m.)

Vertical

10m plus the terminal length – minus any bend penalty. (90° = 1m; 45° bend = 0.5m.)

Note: To dispose of condensate, ensure the fall towards the boiler is 35mm per metre length.

Clearances (min.)

Side: 20mm

Above: 200mm

Flue duct to combustible

material: 25mm

Below: 200mm

In front: 600mm

Gas supply

The supply size from the meter must provide a steady working pressure of 20 mbar.

Bypass

If TRVs are to be fitted to all radiators, an adjustable bypass (in addition to the in-built appliance by-pass) should be fitted not less than 1.5 metres from the appliance.

DHW flow rate

Prior to hanging the appliance, fit the supplied flow restrictor into the outlet of the mains isolation valve. This will govern the flow rate to 10 litres/min (24cxi) and 12 litres/min (30cxi).

Electrical supply fuse

3A.

Room thermostat connection

On the clip-on terminal block on the upper-LH rear edge of the control box. This factory-fitted link MUST be removed before connecting either a voltage free OR mains voltage control. Boiler will operate continuously if link is not removed.

External controls connection

230V AC via a three-pin connecting block (in the fittings pack) onto the 230V interface PCB (see wiring diagram for connection detail).

COMMISSIONING / OPERATION

Filling

Open all water isolation valves and all taps until an air-free flow is attained. Open – and leave open – the pump automatic air vent and open the fill valve. Vent the pump and radiators and allow the system pressure to reach at least 1 bar before closing the fill valve. Check for and remedy any leaks.

Purge the gas supply, open the isolation valve and check for soundness.

Preparation

Set all external controls to call for heat. On the appliance set CH control on and DHW pre-heat off. Remove the inner casing panel and attach a pressure gauge to the gas control inlet pressure test point. Check gas rate using meter and stopwatch.

Note: Burner pressure is not checked as it is subject to fan suction and modulation. Gas control checks and adjustments required following servicing or control replacement are detailed under ‘Combustion Check’.

Lighting

With the electrical supply on, setting the boiler control panel switch to 1 should automatically start the boiler. The fan and pump will start, and after a few seconds the ignition should commence. Observe the sight glass. If the burner fails to light or goes out after initial lighting, the fan will stop but the system will attempt re-lighting a further two times, then lockout. If this occurs, the LCD display will show F1 or F4.

Reset the main switch to re-commence the start sequence.

Note 1: If ‘Pre-heat on’ has been selected, the boiler will initially feed the plate heat exchanger before switching to central heating.

Note 2: (30cxi only). Following ignition on the first light-up at installation or following re-instatement of mains power, the boiler will go straight to full power. Thereafter it will ‘ramp’ (i.e. slowly) to full power.

When lit the boiler will continue firing until the room thermostat (if fitted) or the control panel set temperature isreached. However, if a demandfor DHW is made by opening a tap (or if the hot water control knob is re-selected to the pre-heat mode) the diverter valve will change over to supply the plate heat exchanger. On the LCD the readout will change to show water pressure.

Check that the inlet gas pressure maintains 20 mbar with several draw-off taps fully open. When satisfied, close the taps, remove the gauge and check for soundness.

Job completion

Balance the radiators and system. Flow rate across the boiler should be equal to 20°C differential at maximum heat input. Drain while hot, then refill and vent as before, pressurizing to 1 bar. Refit the inner and outer panels.

SERVICING

The majority of panel and bracket screws are of the Torx 20 type. Pipe connections are generally by plate circlip. This appliance is supplied factory-set and should not require any adjustment other than as detailed under COMMISSIONING/OPERATION. However, should it become necessary to exchange the gas valve or adjust the setting, it must be carried out as detailed under ‘combustion check’ below.

Combustion check (as required)

• Connect a gas analyser to the test point on the flue adaptor.
• Turn off the electrical power and unclip the control panel fascia . Do not allow to fall.
• Set the controls to call for heat and reinstate the power. The boiler will start automatically.
• After a minimum 60 seconds of operation, adjust the ’service’ potentiometer fully clockwise.
• Check the fan speed readout on the LCD display. It should be 41 for the 24cxi (47 for the 30cxi). CO2 should be 8.8 per cent ± 0.2 per cent. (Note: If the air-box front panel is fitted during this check, the CO2 will be higher at 9.0 per cent ± 0.3 per cent.)
• If CO2 is not correct, adjust the ‘throttle’(anticlockwise to increase) to achieve 8.8 per cent.
• Next rotate the service potentiometer fully anti clockwise, hold there for about five seconds, then reset clockwise to the three o’clock position (twelve o’clock is to the rear when facing the boiler). The display should now show a flashing 12 – indicating 1200 rpm fan speed. CO2 should be 8.8 per cent ± 0.2 per cent.
• If CO2 is not correct at this minimum fan speed, very carefully adjust the ‘offset’ screw (one-eighth AF hexagon key) to 8.8 per cent. Adjustment is very coarse
• Now rotate the service potentiometer fully clockwise again to the maximum speed setting and recheck the CO2 reading (8.8 per cent).
• Finally reset the potentiometer fully anticlockwise (display shows water temperature).
• Remove the analyser and refit the test point cap.

Routine servicing

Wherever possible, carry out a flue gas analysis check (see ‘Combustion Check’) to determine the level of servicing required. Where this is not possible or where the check indicates that cleaning is required, remove the burner, fan and gas control assembly.

Check/adjust the electrode (3.5mm — 4.5mm gap) and clean the burner with a soft bristle brush. Carefully vacuum the heat exchanger and combustion chamber, taking care to avoid damaging the front and rear insulation linings.

DHW and CH return filters can be removed and rinsed clean, as required.

Check that the condensate drain is clear, if necessary flushing the trap with water via the heat exchanger or remove for cleaning as described below.

1. Isolate electrical power.
2. Detach ignition and fan transformer units to move aside.
3. Remove circlip under sump and slacken both plastic pipe clips (to provide manoeuverability).
4. Remove screws securing trap.
5. Pull left-hand pipe fitting down off sump outlet.
6. Lift adaptor out of trap and detach from pipes (to provide clearance).
7. Lift trap out of appliance, detaching from drain pipe during lift.

Note: When refitting, ensure felt seal is not misaligned.

After re-assembly, carry out a combustion check.