Incoming not ringing on standard phones, OK on cordless

[#1]

I have 2 standard phones and a cordless  base connected to line (plus internet connection).    Internet connection and 1 standard phone plugged into dual main socket.  Other standard phone and cordless base station are on extension sockets.  Microfilters in place.    System has worked perfectly for years up to a couple of weeks ago.

Problem: 

Incoming:  Calls ring on cordless but not the other 2.  Can be answered OK on  cordless, and once answered, can be picked up on the standard phones.    

Outgoing - all phones have dial tone.  Making a call (from standard phone) rings out OK, but when answered it disconnects.  However  making a repeat call straight away works OK and stays connected.

I am very non-technical.  Help !

[#2]

@Malcolm57  Welcome to the forum.

This sounds a bit like like an impedance fault. Does your broadband drop when the phone is ringing? Report a phone fault:

For a problem with your home phone,

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[#3]

Re: 'does Broadband drop ?' - if as in 'drop out',  then no.  If as in 'drop in speed' - not noticed

Would impedance (afraid I don't know what that means) also affect the outgoing call disconnecting when answered first time, but OK on second attempt ?

[#4]

@Malcolm57  Welcome to the forum. 🙂

By 'dual main socket' I assume you mean a master socket with a filtered faceplate.

If so, the extension sockets don't need a micro-filter, though it will do no harm if they are fitted.

Is there any difference if you remove them?

[#5]

Thanks for reply - yes the 'dual main socket' was fitted a couple of years ago and has separate phone and broadband sockets on the front.  The wires to the extensions are (I assume)  out from the back of this.   Removing the micro-filter for the (extension) standard phone doesn't appear to make any difference. 

A friend suggested the exchange might not be sending sufficient ringing current to activate the standard phones. due to a faulty circuit board in the exchange, but I'm puzzled why this would also cause the outgoing problem of a first call dropping out when answered,  but being OK immediately afterwards with a second call

[#6]

My suggestion would be to unclip and remove the faceplate from the master socket and then reattach it and make sure its properly seated and clipped in. Do it at a quiet time , since it will disconnect the broadband.

The contacts on the later Mk4 dual faceplate are poorer quality than the older ones. Removing and reconnecting will 'clean' any corrosion off the contacts and may fix the problem.