Biasi M96.28SM broken temp sensor and pressure gauge?

[Mendoza81]

Hi,

I'm not a plumber so if this sounds like it needs a gas safe engineer please just say and I'll call one in, but just in case I can fix it myself or to make sure I'm being told the right thing I'd appreciate some guidance.

My Biasi Riva Compact HE boiler (M96.28SM) appears to have 2 faults
1. The frost protection mode comes on for about 30 seconds once an hour (fault lights indicate Faulty c.h. temperature probe NTC when this happens)

2. The pressure gauge was reading approx 0.2 bar. I have tried adding more water via the filling loop and bleeding the rads but the gauge didn't move. It also doesn't move when he boiler is running ( I assume pressure would increase under heating ). Strangely later in the evening the pressure rose to approx 0.4 bar the heating and hot water hadn't been used other than the frost protection mode kicking in a few times.

Other than this both central heating and hot water are functioning correctly.

Can I change the temp sensors myself or is removing the cover of the boiler a no no. I don't suppose boilers are like computers given the amount of circuitry and they just need switching off and on again.

Thanks
Andrew

 

[plumbplumb]

Yep. The temp sensor for heating is quite simple on this model.
It's on the brass manifold in front of you connected by red wires.
Remove all pressure from the system and isolate heating flow/return quarter turn they are the 2 22mm valves at opposite ends of the boiler.

Draw the PCB housing towards you removing all the screws from the underside of the boiler.

Remove and refit sensor.

If your pressure isn't rising and you remove the sensor and it's covered in black gunge it could be blocked on the capilliary tube to the pressure gauge.

This is connected behind the pump. It has a clip holding it and is just pushed in sealed with an o-ring. may be worth pulling it out while the boiler is drained and poking something into it.

Also best to protect the PCB housing with plastic bags just in case.

There is a boiler drain also connected on the pump block on the left behind it.

It it likely gunged up as the boiler doesn't fire without sufficient pressure/pump flow.

 

[Mendoza81]

Thanks for the detailed reply it sounds like something I could cope with so that'll be my weekend sorted.

 

[Agile]

Before you replace the sensor slowly remove and replace the plug a few times. Sometimes its only a bad connection.

If that does not cure it then try to measure its resistance with the boiler cold. It should be about 13 k.

The pressure gauge tube often blocks at the boiler end and can sometimes be unblocked with a needle. But the connection is rather fiddly and not even something I relish.

You may well just have insufficient pressure in the system!

Tony

 

[Mendoza81]

Thanks for the responses, it seems like low pressure was causing the frost protection issue and gunged up pipes might be the culprit for the pressure gauge.

24 hours after adding water via the fill loop, the pressure gauge had gone up to 2 bar and was sitting steady and the frost protection was now working correctly.

I drained a few jugs of water off one of the rads and after about 12 hours the pressure gauge had dropped of to about 1.6 bar, frost protection still working correctly at this time, so seems the pressure gauge is slow to respond.

I'll keep an eye on it and get the engineer to take a look at the pipes to the pressure gauge when its serviced.

Again thanks for the guidance.