Blocked flue

[solent]

I have a gas warm air/water heating system. Last week I got the gas man in to service it and he reported a blocked flue and disconnected the equipment. Despite me phoning to chase him I can't get him to return my calls to say what to do about it.

I'm considering calling in a chimney sweep and then get another gas man to reconnect and retest.

But, I assume the burners (already disconnected) and heat exchangers will need to be removed before the sweep can get to work to prevent them being blocked with the sweepings. Is this something I can expect the sweep to do, or would I have to do it/get it done first?

Also, the water heating uses a gravity fed system. Two pipes from the heat exchanger below to the cylinder above, but I can't see any connections for refilling (or indeed, venting). Is this possible? or must there be something hidden under the floorboards in the bathroom (the only part of the system I can't access)? If not, I have no idea how I would set about refilling it. (BTW the house was built in 1984).

 

[penpusher]

A chimney sweep wont be able to unblock that type of flue as you'll most likely have a twinwall flue. My advice would be to get the lot ripped out and replaced. These Warm Air Units are past their best and cost a fortune to repair. If your engineer wont return your calls then I doubt he'd be the best to replace it though.

 

[solent]

The flue goes vertically up through the roof (with a couple of slightly angled joints in the roofspace). Isn't a twinwall flue the type that goes horizontally through a wall?

 

[corgiman]

I love warm air I do

the fans can be dear but not as much as a new Potty PCB

how did the chap decide on a blocked flue?

 

[Dan Robinson]

Isn't a twinwall flue the type that goes horizontally through a wall?

You're thinking of concentric. We are talking about twinwall.

[/quote]

 

[solent]

how did the chap decide on a blocked flue?

He used a couple of smoke generators which showed the smoke refusing to go up the flue in both the air and water burners (says 'spillage' on the red tag).


I've looked up twin wall on google, and yes, it looks like one of those.

I take it a new flue means ripping apart the walls to get to it. Ouch!

 

[Gasguru]

You need to clarify exactly what is meant by a blocked flue. The flue should have a terminal on top that should prevent any ingress of debris.

Perhaps he did not fire up the unit and get the flue warm before smoke testing. The heat exchangers are very restrictive where they meet the draught diverter and are often reluctant to draw when cold. In addition some manufacturers eg J&S may not require an initial 600mm of vertical flue off the unit and again this doesn't help the flow.

Did he inspect the flue throughout its full lenght?, perhaps its collapsed and lying on the ceiling in the roofspace.

A chimney sweep is not going to help...drain rods could damage the flue, you could end up popping a joint if its 100mm twin wall. 15mm plastic pipe would be better. Better still a drain camera.

As for fans always used CET since J&S are a rip off.

What is the make/model of the unit?

 

[corgiman]

Top tip Guru

I will try them for the fans

OP where are you in Hants?

 

[solent]

He determined it was a blocked flue by using a couple of smoke generators which showed the smoke refusing to go up the flue in both the air and water burners (says 'spillage' on the red tag).

I don't know if the unit was fired and left to warm up. I wasn't watching what he was doing, but I suspect it wasn't, or at least wasn't left on long. (Both burners where set to pilot at least 24 hours before his arrival).

The ar heater is a J&S J15-22R. The water a J&S Janus-3.

A little back story: The water heater hasn't worked properly in the five years I've owned the house and I've always used the immersion heater. The water heater, if turned to maximum, the flame would spill out from the burner, heat the pipes and cause crackign noises as the pipes expanded. If turned down it didn't heat the water sufficiently. After switching back to the gas water heater it had the same fault as before, but one day last week there was a rather horrible burning smell filling the house, so I switched the unit to pilot and called the engineer.

The air heating has always worked. Neither unit has been serviced since I bought the house (Sorry, never got around to getting it done) but I have fitted a new fan and timer.

 

[solent]

I should add, he looked in the loft at the flue and never reported any problems (I've looked myself and can't see anything obviously wrong). The rest of the run is concealed behind walls.

I'm located in Fareham (Locks Heath)

 

[Nige F]

those were fitted by old "Bo" the plumber back in the 60`s...he liked his blow, did Bo....used to be stoned most of the time .........Bo-Lox Heath, heating + plumbing co.

 

[Gasguru]

He determined it was a blocked flue by using a couple of smoke generators which showed the smoke refusing to go up the flue in both the air and water burners (says 'spillage' on the red tag).

I don't know if the unit was fired and left to warm up. I wasn't watching what he was doing, but I suspect it wasn't, or at least wasn't left on long. (Both burners where set to pilot at least 24 hours before his arrival).

If the flue was not warmed up it may fail the flue flow test due to reasons listed above. Most flues on warm air terminate with a ridge tile and once hot will draw well. It is normal to run the burner for 5 minutes to heat up the flue prior the the flue flow test. The burners are extinguished during the flow test - a smoke pellet is used to check the condition of the flue. Ventillation must be compliant and doors/windows closed.

After servicing the unit and it is reassembled a spilage test is carried out. This is to check the flue is operating correctly with the burners ON. It is normal to allow the flue to warm up prior to testing. 5 or even 10 minutes running is allowable before testing commences.

However on the J&S units a different approach to spillage testing is often carried out. Because the draught diverter is at the back of the unit and inaccesable spillage testing is slightly different. The unit is allowed to heat up and the burners then extinguished. Smoke is then introduced to the air intake to the burner. The unit is checked for smoke at the draught diverter with the fan running and stopped; any escape would indicate spillage.

Another reason for spillage is a split heat exchnager or missing/perished seals on the unit.

The water heater hasn't worked properly in the five years I've owned the house and I've always used the immersion heater. The water heater, if turned to maximum, the flame would spill out from the burner, heat the pipes and cause crackign noises as the pipes expanded.

The Janus and similar water heaters (circulators) are notorious for the heat exchangers blocking. Due to an open flue design they easily block with combustion products. When this happens they overheat and the flames will spill out from the burner. They are often not serviced properly (its a long boring job) and many circulators are disconnected due to serious overheating.


I suggest yoiu check if the flue was warmed up for testing.

A proper service and saftey check on a warm air unit with a circulator will take a couple of hours minimum and should be done every year.