Baxi 105 HE problems

[Jaybob]

Hi,

I have a problem with my Baxi 105 HE combi boiler. I've searched these forums (and others) and see that folk have had similar problems before but not all at the same time so I decided to post.
Sorry if I should have followed any previous solutions but didn't want to screw it up worse.

I've outlined the symptoms below, any help and sugestions would be greatly appreciated. My house is a 3 bed terraced with 4 rads upstairs and 4 downstairs. I removed all the thermostatic rad valves and made sure the pins bounced nicely. The boiler is on the landing.

A friend said it could be the pump so i replaced it today with a refurbished one from National Boiler Parts, Tyne and Wear, alas no effect

No warning lights or dodgy sounds. These symptoms were the same before and after I changed the pump so i'm sure it was fitted correctly.


CH (all HW taps off)
warm upstairs / cold downstairs, or vice versa.
with the CH dial at 2/3, burner comes on, temp goes up to 90 (all lights) burner cuts out, cools to 20 (2 lights) then repeats.
with the CH dial at 1/3 same as above but cuts out at 60 (4 lights)


DHW (CH off) bathroom hot tap on full
with the DHW dial at 2/3, burner comes on, temp goes up to 90 (all lights) burner cuts out, cools to 80 then repeats. but water feels much cooler than that. I can keep my hand under the water all the time.
with the DHW dial at 1/3, same as above.

Any help and suggestions are most welcome, if you need more info just ask.

EDIT:
I just read that the expansion tanks can need recharging, should i have done that when i changed the pump?

Thanks
Jay

 

[gigz]

Sounds like a blockage. Possibly plate hex scaled up. Flat expansion vessel would show on the pressure guage.

 

[gigz]

P.S. Turn the heating off, turn on a hot tap then feel the flow pipe (22mm copper on the left hand side of the boiler).

 

[petit_pablo]

Id say main heat ex is blocked if its doing that on both CH and HW. I imagine its quite noisy whilst the burner is on too.

 

[FlyingFish]

As the rapid temp rise is happening on both ch and dhw then I would say you have a blockage or restriction. And going on experience it will be at the bottom of the flow pipe from the primary heat exchanger where it elbows into the diverter valve. This is on the left of the boiler. The fibre washer has a habit of collecting sediment. I would also take the opportunity to clean the strainer on the return iso valve.

BTW easiest way to clear the port is to remove the pressure differential, then remove the large gland nut behind and use some plumbing solder to carefully 'rod' around the corner into the pipe through the diverter valve front. Its a bit crude but gets the job done without stripping and disturbing too much and causing leaks (esp the heat exch seal above). You could do it the proper way and remove either the flow pipe or diverter valve, but that will involve replacing seals and taking longer.

Once back together get some cleaning chemical in the boiler to desludge the rest, then protect with inhibitor.

 

[gas112]

CH FAULT CHECK FILTER IN RETURN VALVVE AND CLEAN .
HW FAULT REMOVE PLATE HEAT EXCHANGER DESCALE WITH BRICK ACID AT SAME TIME REMOVE THE DIAPHRAGM HOUSING. then remove the big castated nut behind it the pin that comes through this will have crude on it clean it up with wire wool silicone grease the pin and o ring on spindle re assemble all done in less than 1 hour.
You can check and recharge expansion vessel at this point before refilling system

 

[Jaybob]

Thanks for all of the replies, i have a couple of questions.

@gigz - The CH flow pipe remains cold and the DHW flow feels the same at the water at the taps, i can hold it continuously.
Thanks for the expansion vessel tip.

@petit_pablo - it sounds quite normal actually, there's no percolating sounds so i'm thinking the flow is stopping/starting rather than gurgling through (or no air?).

@FlyingFish - what's a "pressure differential" i can't find it in the service manual.

@gas112 - i removed the end cap to examine the filter, i can't see how to remove the filter to clean it? or should i just use a bottle brush?

 

[FlyingFish]

Big round brass assembly on the left of the boiler with two 10mm pipes in the top. Held in place by two small grub screws behind.

And that gauze strainer in the return ISO valve just slides out for cleaning.

 

[Agile]

It really sounds as if your boiler has become very dirty inside and probably your system too.

Whilst you can clean the plate HE and the return filter, I would certainly recommend you use some cleaner inside the boiler itself.

You can do that by using something like citric acid in the boiler and using it for hot water and a little time on heating but with the CH flow valve closed.

But this is quite extreme for DIY repairs although nothing very specialised involved.

Tony

 

[Jaybob]

This filter seems to be pretty stuck. if finishes flush with the fitting that its inserted into with no lip so nothing to get a screwdriver under. I've inserted a bladed screwdriver at an angle and tried to drag it out but to no avail. Does anyone have any hints n tips for removing it?

EDIT
@Agile - sorry, i neglected to thank you for your input. If i can get this filter out i will then clean the HE and come back for details about getting cleaner into the boiler.

 

[FlyingFish]

Grab it with needle nose pliers and pull But echoing everyone else's advice, all this and the struggle your having getting the strainer out really does indicate a poor sludged up unhealthy system. I'd be looking at ds40 and power flushing.

 

[Jaybob]

Thanks, I inserted a small flat screwdriver between the gauze and fitting and gave it a little twist to separate the two, then the pliers trick worked sweet.
The filter was very black but there was very little build up inside the tube, no more than 1mm thick and only in "spots" i could see light through the gauze (from the side)
It's now shiny clean and refitted.

I'm going to clean the HE next, power flushing has been floating around in the back of my mind but to be honest i can't really afford it, especially in January.
why is power flushing so expensive? Is there a poor mans alternative? I could afford maybe £200 but not the £300+ that it's going to be.

 

[FlyingFish]

Then I would recommend fitting a magnaclean pro2 to the return pipe under your boiler, adding cleaning chemical perhaps x400 or x800 depending on your needs/time and then cleaning the filter as the chemical breaks the sludge down. The filter will remain and keep the boiler clean as best it can.

 

[Jaybob]

I didn't get chance to clean the HE today so it's postponed until tomorrow when the light returns, however the difference to the radiators from cleaning that filter is massive. All rads are hot with no cold spots and the boiler isn't hitting 90 and cutting out! I've had to back the dial off to 1/3 because the rads are that hot!

Fantastic!