Warmcair CD and CU Johnson and Starley warm air boilers:

 

C10D, C16D, C26D, C16U, C26U

 

The Warmcair CD and CU range of boilers introduced in 2016, is a ‘ground-up’ revision of the gas warm air boiler format. All the old lower-efficiency ranges are now  gone and the new Warmcair boilers are ‘high efficiency’ condensing boilers with dual concentric flues meaning they burn less gas, produce less air pollution and do not need a draught-producing fresh air vent to outside. There are broadly two types of Warmcair: those that are air heating only, and those that heat water as well. The two types work in different ways. This page deals with the heat only versions. The hot water versions are on the other page which I may not have written yet! The C10D, C16D and C26D are downflow boilers, i.e. the warm air output is through a duct connection in the base of the boiler for warm air ductwork starting off concealed in the floor of the house. The C16U and C26U have duct connections from the top, for ductwork starting at high level e.g. in lofts. The number indicates the heat input rating in kiloWatts.

 

The warm air only versions are quite simple boilers although somewhat unconventional, in the way the gas valve and inlet Venturi are located separately from the combustion air fan. A gas and air mix is drawn into the burner and combustion chamber low down in the boiler where it heats a large drum over which house air is blown for heating, then the slightly cooled combustion gas passes up to a second, multi-tube condensing heat exchanger higher in the boiler where most of the remaining heat energy is extracted and the water vapour in combustion gasses condensed out for peak fuel efficiency. The warm circulation air is blown through the boiler by a fan which varies in speed to match the heat load presented by the house to the boiler. The heat load is determined from the room temperature sensor using a digital protocol called “OpenTherm”, which is all well and good when working but over-complicated (in my personal opinion) and a complete mystery when it stops working. There is no alternative though, you have to use an OpenTherm protocol room sensor. 

 

Most of the problems the Warmcair suffers from revolve around the condensate liquid produced. It leaks out, the pipes block and the drain pump fails in a variety of ways.

 

 

Common faults and fixes:

 

1) Condensate leaks:

 

I have seen several of these boilers with significant corrosion inside at the base caused by minor leaks from the gasket which seals the combustion collection box in place. The collection box is moulded from a tough plastic fixed in place with a number of screws, which I think cause the shape of the box to gradually creep as it grows older, meaning the sealing gasket no longer accurately fits and seals, causing the leaks I see. Another source of condensate leaking is the outlet hose connection onto the condensate pump embrittles with age and heat then spontaneously cracks or completely snaps off. When it snaps off the big leak creates a perverse boiler failure. The pump runs but the leaking condensate flows directly back into the condensate collection chamber keeping it full despite the pump running. This means the condensate pump runs all the time and boiler electronics notices this and turns the boiler OFF!

 

 

2) Failure to light:

 

I’ve seen failure to light just twice on this model of boiler. Once caused by failure of the “ESYS” ignition control module ‘piggy-backed’ onto the gas valve and a new ESYS module fixed the fault. The second time was a loose connection onto the ESYS module. The flame sensing electrode lead was not pressed onto the tag so not making a proper electrical connection, causing the flame failure errors 1 and 26. 

Edit to add: I’ve also just seen a fast flashing red lockout light and Error 45 (open circuit flue overheat sensor) which also turned out to be a poor connection onto the red ESYS module on the gas valve. Conductor No 9 in the multiway connector. A common problem or I’ve been advised by J&S. 

 

 

3) Condensate pump failure:

 

This boiler produces waste water as a by-product of its high fuel-efficiency. This dribble of waste water is known as ‘condensate’ and needs to be routed to a drain. Wall-hung boilers generally rely on gravity for this but the Warmcair boilers being floor standing and often fitted as replacements for older, non-condensing boilers not near a drain, need to be more flexible. So they have a pump to expel the condensate through a thin tube up to about ten metres long which can run vertically up to a drain connection several feet higher than the boiler. In a first floor bathroom for example. The drawback of this is eventually the condensate pump fails and the boiler stops working. A new condensate pump is needed and I carry them in the van nowadays as this is becoming more common.

 

 

4) Blocked condensate restrictor:

 

I’ve seen no mention of this in the manual but there is a flow restrictor fitted into the condensate drain tube leading from the main heat exchanger down to the condensate pump. This blocks up leading to the heat exchanger one-third filling up with condensate which must substantially reduce the heat output of the boiler! The combustion air fan is removed during routine servicing and looking through the hole where the fan was fitted, one can see the heat exchanger full of condensate up to the level of the fan, caused by the blocked restrictor. Quite shocking to see. The restrictor is a red plastic component inside the condensate pipe just where it enters the drain pump. It has a hole about 2mm in diameter which needs checking at every service, in my personal opinion. See photo.

 

 

5) Air noise:

 

This is not really a fault but a complaint from a user, and relates to the C16D specifically. The fan in the C16D is only half the size of the large, quiet fan in the equivalent old Johnson and Starley boiler replaced by the C16D, meaning the new boiler fan needs to run at twice the speed of the old, with consequently twice the noise. The only solution I can think of is to reduce the maximum fan speed within the configuration menu in the boiler. This is not really satisfactory as reducing the fan speed also reduces the boiler heat output, but it will probably fix the problem for this family.

 

 

6) Flue terminal noise:

 

I’ve encountered one where outside, the flue terminal makes a constant loud monotone humming/droning noise, audible outside in the garden and from the road outside the house. It cannot be heard inside, but the owner is concerned that sooner or later a neighbour will complain. I’ve yet to investigate why, but is probably caused by the combustion settings on the gas valve drifting out of adjustment.

 

7) “Sensor error” fault message and boiler will not run: 

 

The error message “46” (flue temperature sensor open circuit) is known to be caused sometimes by a poor electrical connection on the red-boxed PCB ‘piggy-backed’ onto the gas valve. (Terminal 13 from memory) Flue sensor is not actually open circuit when measured, but the boiler thinks it is due to the poor electrical connection at the other end of the wiring.

 

 

Finally, the user display on these boilers is very un-intuitive. If the boiler breaks down or stops working, you’d expect it to display a clear error message but no, it is a tiny little letter “e” on the screen you’d barely notice unless you look hard for it. When the ‘e” is present, a proper fault code will be displayed if the “RESET” button is pressed in and held down for more than one second, then released. The fault code can then be looked up in a chart in the boiler manual to find out what has actually gone wrong. The chart in the manual is long but here are some of the most likely faults, abridged by me to fit on the page:

 

N/A: No call for heat

1: Flame failure lockout. Repeatedly failed to light

2: False flame detected so locked out

3: Condensate pump failure

4: APS open - Air circ fan not running (not CAF)

5: No tacho from CAF (CAF failure)

7: Flue gas over-temp

8: Flame sense lead shorted to earth

9: Gas valve not detected (ESYS error or GV fail)

13: Exceeded 5 remote resets per hour

21: ADC error (change ESYS)

25: CRC error (change ESYS)

26: Flame detection lost 5 times in four mins 

 

There are also some “Blocking codes”

30: Duct air temp sensor shorted to earth (condensate leak)

31: Duct air sensor open circuit

43: Return sensor short circuit

44: Return sensor open circuit

45: Flue temp sensor short circuit

46: Flue temp sensor open circuit

57: Airflow temp too high (check filter and vent grilles)

99: ESYS comms lost

 

 

If your Warmcair boiler has broken down and needs a repair, call or text me on 07866 766364.

 

Mike

 

 

 

 

 

 

 

 

 

Menu:

Photo showing the condensate restrictor location. During servicing I suggest pulling the red plastic condensate restrictor (on the red arrow) out of the “Y” adaptor to make sure the 2mm hole is not blocked. If blocked, the boiler cleverly senses the blockage and turns itself OFF which, less cleverly results in a breakdown callout. No mention of this in the service schedule.