Baxi Combi Instant 105e problem(s)

[stustu92]

Hi,

When i turn on a hot tap the boiler supplies DHW, but at the same time the central heating circuit starts getting hot too.

For example if the bathroom shower is used for 5-10 mins the upstairs radiators get hot.

Also the central heating circuit (supposed to be sealed i believe) is losing pressure to the point where i have to top it up every couple of days.

To top it off last week the boiler sounded like it was running continuously when there was no CH or DHW demand for a fair while. I checked it out and the CH pressure gauge was reading just over 3 bar... So i drained some water out of the drain point on a downstairs rad.

Any ideas why?

 

[45yearsagasman]

Very common problem. Your diverter valve requires an overhaul. There is a kit available. Kit 760.
Your pressure problem could be the expansion vessel has either lost its primary charge or it has failed internally.
A continual rise in pressure when the boiler is off could be the plate heat exchanger has also failed.
Lots of things to check. Are you going to DIY?

 

[stustu92]

yes i plan to. I've just had the DHW diverter valve cover off to check the diaphragm. It looks ok to my untrained eyes...

shall i do the CH diverter next?

 

[PlumbGas]

yes i plan to. I've just had the DHW diverter valve cover off to check the diaphragm. It looks ok to my untrained eyes...

shall i do the CH diverter next?

It's not the diaphragm your looking for, it's the back end of the valve as you look at it the CH section, You'll need to drain down boiler to repair

 

[45yearsagasman]

View media item 31064This will get you started

 

[stustu92]

Thanks for the image of the valve.

Unfortunately i found i was unable to progress with disassembling the valve/manifold any further than looking at the diaphragm as i couldn't drain the primary circuit fully.

I used the all of the isolation valves at the bottom of the boiler, turned main stopcock off, opened and drain hot water circuit and open the drain cock on the lower right hand side inside the boiler. This drained about a quarter of a bucket out but then just about stopped. It just made glugging noises every so often and a little more water came out of the drain cock.

At this point i started trying to check the CH diverter valve diaphram and water just kept coming out when i undid the screws.

Can anyone offer any suggestion of how i could drain the thing fully?

 

[ChrisOxford]

Absolutely no water coming out of any of your house's cold taps?

And are the valves that isolate the flow/return to your radiators definitely fully off, i.e. screwdriver slot at exactly 90 degrees to the pipes?

You may need to let air into the boiler to get the last of the water out. Have you read (and followed) the Manufacturer's Instructions?

 

[Agile]

That normally means its as empty as its going to get.

When you disconnect the diverter a bit more water will come out and you need to be prepared to catch up tp about 1 litre perhaps.

Tony

 

[stustu92]

@ChrisOxford - i didn't empty the cold water pipes, just turned of the main stopcock. Should i have emptied the cold pipes by opeing the house taps?

one of the CH flow or return isolator valves wouldn't quite close properly so i went and drained a little water out of a downstairs rad. I would have thought a few litres would be enough?

I have the Baxi installation/service manual for my boiler and in the section showing how to change components it continually makes reference to draining the primary circuit. But there is no explicit instruction of how to complete this.

@Agile - i have read about expansion vessel diaphrams failing on this boiler and suspect that mine has failed so i was just a bit cautious about undoing anything too much if i have a EV full of water which could come out.

I'm just wary with water still coming out and the boiler electrics being sat where the water would probably want to go.

Do you have any further advice how to completely drain it?

Thanks to you both.

 

[Agile]

You never told us it was an instant !!!

When draining pressurise the air in the EXV and this will help force water out of it.

Tony

 

[stustu92]

@Agile - i didn't realise until you your last post that there was a difference between a Baxi Combi 105e and a Baxi Instant Combi 105e.

Been thinking about the boiler today.

We've been in this house about 6 years and even when we first moved in the CH circuit would lose pressure to need topping up every couple of weeks. We just assumed this was normal for a combi boiler as our last house had a back boiler.

Can't say for sure but i bet the boiler had been in a few years before we bought the house also.

Working on the principle that any corrosion inhibitor probably left the system a long time ago would it be fair to assume that the whole workings in the boiler would be full of sludge?

I'm working on the assumption that the diverter valve needs replacing, the expansion vessel will need replacing and possibly the plate heat exchanger as per 45yearsagasman's comments...

Would it be economical to repair these things or is it new boiler time?