Halstead Quattro & fluctuating water temperatures

[RobF]

First of all you should know that I know nothing about central heating or boilers.

Here is our problem:

We have an 8 year old Halstead Quattro boiler which prior to us installing 2 x Mira 415 showers in May last year seemed to work perfectly i.e CH & HW

During the installation of the showers the PCB on the quattro had to be replaced.

Since then we are unable to take a shower OR run taps (upstairs or downstairs) without the water eventually running cold. CH is always ok.

There seems to be no pattern to this apart from we seem to be ok first thing in the morning when the CH has not been on for long. Anytime from 8.00 in the morning until 8.00 in the evening it can be a lottery - sometimes the water is hot. Sometimes it is stone cold. *There is no pattern**

Since May we have spent over £300 on the following parts:

PCB
Diaphragm
+ labour


We have had 3 Corgi registered engineers take a look at it and each one has diagnosed something different. The latest diagnosis was that it needed to be cleaned and the 'heat exchanger' swapped!

We do not want to have to replace the boiler in we can help it (funds are tight) but it looks as though this may be the only option. How many more Corgi engineers are we going to have to try???

Some things I have noticed to aid troubleshooting:

We invariably have our CH on and it is fine
The green lit is always lit (but does not seem to be 'firing' when water is cold)
Pressure is always between 1 and 2 bar
Cold water problem applies to taps upstairs and downstairs (as well as shower) *even when showers are not being used*

Any advice welcome

Thanks

PS Is there anything I can do to get a final, conclusive verdict on the problem EG British Gas???

 

[Bahco]

Have you checked your mains water supply. The supply may be inadequate during different times of the day.
Your boiler would not affect the cold supply but you do seem to be having problems with your mains supply, so this needs checking

 

[ChrisR]

a final, conclusive verdict on the problem EG ***** ***???

Sure. Buy a new boiler

But hell no, it's not a particularly sophisticated thing.
On top of where the diaphragm goes, there are a couple of switches, which you can see. OK? Next time the water is cold, see if the plunger has come out from the brass bit enough to push both(?) switches. If not, diverter valve needs checking.

If they are pushed but no HW, then the switch(es) may be dicky.

If the switches are being ellectrically operated but the boiler isn't firing it'll probably be because it's too hot, probably because of scale in one side or the other of the secondary heat exchanger, which is cleanable (acid). That can be diagnosed by a boiler bloke with a contact thermometer.