E9 error ( WB R35 HE +). (Heat exchanger T.O.C open circuit)

14 Dec 2012
Reaction score
United Kingdom
E9 error on a WB R 35 HE Plus condenser.

I have found the cause of the E9 error.
The Heat Exchanger safety temp limiter is going open circuit when the Heat exchanger surface temperature near the sensor reaches 112 deg C

I have no idea if this is the correct trip temperature or if the sensor is faulty and therefore don't know if there is a fault that is causing this

The appliance hasn't been serviced since new (I know, very bad of me)


The bolier is 8 years old

The symptom:

When running hot water on full flow (Bath tap fully opened) It shuts down after a few minutes and displays E9 error and the tap water then runs cold. I can reset the appliance and re run it. It will consistently error again
If the tap is turned down to a slower rate it doesn't error and I get a lovely hot bath
Having the CH on or off makes no difference

According to the manual, E9 is the Central Heating Safety Temperature limiter activating.
and the steps it advises I take are:

1) Check pressure
(The expansion vessel air pressure is 0.75 bar as per a tyre pressure gauge and the system pressure is okay according to the built in gauge)
I also emptied and then refilled the expansion vessel air bag
I also drained the refilled the boiler and bled the boiler (From what I can gather, this simply means opening the expansion vessel bleed nipple.
I also bled all the radiators

2)Check safety limiters.
..... a) (I temporarily removed the CH flow thermal cut out from its housing so it couldn't sense the CH flow temperature and ran the bath.)
..... b) (I checked the pipe surface temperature at the point where the Hot water NTC sensor is fitted (Same temp as hot water at tap outlet depending on flow rate of the bath tap. At full flow, bath tap fully open, 40 Deg C and at lower flow rate 60 deg C)
..... c) (Heat Exchanger safety temp limiter. Surface temperature at E9 error point is 112 Deg C (No idea what temperature this is supposed to trip at)))

3) Bleed appliance
The service manual doesn't actually state how to bleed the appliance, so I just and made sure the automatic vent on the expansion vessel was open. It was closed (Some air did come out but no water, is this correct ????).
I also bled the radiators, one of them needed badly bleeding (Upstairs bathroom towel radiator)

4) Check fuse on PCB
All 3 checked with a multimeter , not just visually.

5) Check Pump Operation. Don't know how to check it is working at its optimum rate, however it must be working, otherwise the water pressure would be abysmal right ??


Just in case this has any bearing on the issue
We have been constantly topping up the water via the fill hose. (Water dribbling out the PRV vent pipe).
At one point, I accidentally left the fill hose connected and On, then started the boiler up. As you can imagine, the pressure gauge went nuts on me for the 3 or 4 seconds it took me to realise what I had done.
I have since (When I eventually got round to it) stripped and cleaned the PRV and this has reduced the amount of topping up we need to do by quite a lot.

Anyone got any thoughts for this

PS. I am a Gas Safe service engineer, I have my boiler ticket, I just don't work on them (Cookers and gas fires) so have little if any experience on them. I thought i'd drop that info in, just incase you may be reluctant to give me any real guidance
Sponsored Links
Terox, we are happy to give you advice on gas matters but only inside the CC part of this site which you can sign up for if you are registered!

Before you post here you are deemed to have read the site rules which say no DIY gas advice!

Where do you get a tool to fit the bypass on the coaxial knob used on many hobs?
Sponsored Links
Where do you get a tool to fit the bypass on the coaxial knob used on many hobs?

The company I work for gave me one of these as part of my toolkit.
When it broke, I bought the thinnest fine flat point i could from B&Q, which was an electrical screwdriver. I had to shave the insulation off, so that the metal part of the shaft was long enough to reach inside the tap stem and engage with the bypass screw.

Thanks for the advice, have applied for the CC

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local