Baxi Combi 105e (not Instant) CH not getting hot

[MrLee]

Hi

We have a 8 year old Baxi 105e which came with the house.

Recently, we have noticed that only the radiators closest to the boiler are getting warm (but not as hot as they used to), and all the others are staying cold.

I've had a look at the boiler and when the ch starts, it gets hot very quickly (30 secs - 1 min) and shuts off. The pipes coming out of the boiler are too hot to touch, so i don't think it is a faulty thermistor.

Once it has cooled down to 30-40 degrees, it lights back up again and repeats this cycle.

There are no flashing warning lights.

The temperature lights on the control board seem to reflect the heat of the flow pipe.

When only the CH is running:
On the diverter valve, the CH pin activates the switch ok, and the HW pin and switch stays off.

The HW plate exchanger gets hot - is that normal?

Once the flame has cut out, the pump continues to run and the CH pin and switch stay activated.


So far, i've tried the following:

Tried bleeding and re-balancing radiators
This made no difference. I even tried forcing the warm water to the living room radiator by switching all the other radiators off, which didn't work.

There was no air in any of the rads.

Put cleaner in the system and flushed through.
This made no difference, although it did work its way through the system (you could smell the cleaner in the fluid of all the radiators). Also, the water was very clean when I drained it out.

Checked the pump
I took the head off and it's spin is very strong (could'nt stop it with my finger at all). Inside the other half of the pump was not blocked and just had a bit of black residue on the sides.

Checked the divertor valve diaphragms
I checked these thoroughly and, although a little scaled, there are no tears or holes. While I had the diverter valve out I gave it a good rinse and this did not have any sludge in it at all, just a bit of black sediment around it's innerds.



The hot water works perfectly BTW (touch wood )

Does anyone have any idea what could be causing this?

Any suggestions would be much appreciated.

 

[Agile]

Didn't you remove and clean the filter fitted into one of the CH isolating valves?

It should be on the return but about a third I see have it on the flow.

I also saw one on the flow with the filter element missing!

Where can I get a new filter gauze?

Tony

 

[MrLee]

There doesn't seem to be one.

There's a nut sealing off part of the flow isolation valve which looks like it should contain a filter, but there's nothing inside.

 

[MrLee]

You where right Agile - thanks for your help.

After double checking everything and going over it all again, i managed to find the filter gauze and it was completely clogged up. I gave it a good clean, refitted it and now the house is hot again!

I'm surprised that the filter doesn't appear anywhere in the servicing guide.

For anyone who doesn't know, you have to disconnect the feed pipe from the return isolation valve (which is on the right of the boiler) to get to the filter. It looks like there shouldn't be anything there.

The new diverter valve has also fixed the hot water/ch problem, so changing it wasn't a wste of time or money (well, that's what i'll keep telling myself )