Question about RTO X-40 High Output On-Demand water heater & hot shower

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Back flow of fumes

We have had to change the flue to meet current requlations. Now we have a problem with a back flow of fumes from our on demand water heater. The engineer says there is nothing that can be done.

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Your on demand water heater is supposed to be on a seperate vent, directly outside,and not closer then 60 inches from any other vent, the on demand pulls cold air in on the outer side of the vent and blows the hot air out the center of the flue

Posted on May 29, 2009


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The boiler says there is a problem with the fan or flue?

You should be able to hear if fan is running. If it is running & not making squeaking or grinding noises, most likely the flue (pipe that exhausts fumes outside) is plugged. Bird nest, beehive or some other restriction.

Jun 15, 2010 | Water Heaters

1 Answer

Worcester combi gas boiler 3.5 highflow is constantantly dripping water at the external flue position over flow pipe

water vapour is one the main products of combustion of gas. With a standard efficiency boiler, upon initial heat up when the flue is cold this vapour can condensate on the inner wall of the flue but should stop once the flue heats up, to stop this condense dripping back on to the heat exchanger the flue should be tilted towards the outlet and thus on initial heat up water can drip from the flue. with high efficiency (condensing) boilers, condensation will occur in the flue and secondary heat exchanger during normal operation, dispense of this condensate is accommodated for in the boiler and therefor the flue should be tilted towards the boiler, if not the flue will drip constantly.

Apr 06, 2010 | Water Heaters

1 Answer

I have a johnson & starley 25-30 modairflow

I have resently had the same problem.
called british gas to inspect the system and they found that the flue had corroded at the vent and become detached allowing corbon monoxide fumes to enter the roof space and filter down the heater causing it to cut out.
advise you to stop using heater imidiately and call for assistance befor you are all gassed.

Nov 25, 2009 | Water Heaters

1 Answer

I have a vokera unica 28 which pulses when firing

your fan may need attension fan runs after boiler shuts down is normal on some Vokera,s too clear fumes out the flue 2mins approx

Oct 04, 2009 | Water Heaters

1 Answer


your flue is clogged need to clean it, and also need to clear the intake around the combustion chamber===burner


1 Answer

Blower not turning on

push the priority button unplug the unit for 1 min,, plug it back in set the temp to the lowest setting it has to start on the lowest setting turn on a faucet on the hot side, turn it on set the temp after it comes on and it should stay on,, if not check the vent make sure there is nothing around it on the outside it can not have anything blocking it,, all the flue connections have to be in the same way they lock into position and it can determin thru the computer if they are not together it draws in the exhaust fumes and shuts it self down

Apr 10, 2009 | Rheem Tankless Hot Water Heater...

2 Answers

No Hot water

Does the unit light manually with a match while the igniter is trying? If it does the problem may be the same as on my personal Bosch 1600H:

I can't guarantee this will fix yours, but it did fix my Bosch 1600H:

I have positively identified the cause of my problems and know how to fix it.


I opened the side of the seven inch diameter tee that goes to my old conventional heater, and it lights every time regardless of wind. I held a paper up to the open side of the tee and it sucked up and closed the opening and stuck there from the suction. Evidently I had so much draft that the little bit of gas from the pilot was being sucked right up and out of the flue before it could light.

I will re-do my vent to leave an opening to prevent suction from being concentrated in the Bosch. Our tests with this idea have yielded a perfect ‘firing record’!

Add a tee to your flue (you will have to cap it or add an elbow to take it below the outlet of the tee before using the heater, but it needs to stay open for a couple quick tests). Take a flat sheet of typing paper and see if it will '****' to the open branch of the tee and remain there. If it does you may have too much suction (draw) in the flue. The strong suction does not allow the gas of the pilot to light before the gas is dissipated up and out the flue. With the paper removed (SIDE OF TEE OPEN TO THE ATMOSPHERE) test to see if your heater lights every time. If it does you have the cause--TOO MUCH DRAFT. Add an elbow pointing down to the side of the tee. If you want you can put another 1-foot piece of pipe in the bottom of the elbow, but it really only needs to grade up to the flue that goes out of your house to keep flue gases from entering your home.

We just proved this today with my heater, and I am SO HAPPY ABOUT IT!

Mike Wenger

Apr 04, 2009 | Bosch 1600H-NG Natural Gas AquaStar...

1 Answer

Bosch 1600H won't work on windy days

The incorporation of an anti-back flow, flue pipe insert may be your solution, also the pilot flame control may need to be adjusted up a little.

Good luck

Mar 24, 2009 | Bosch 1600H-NG Natural Gas AquaStar...

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