MYSON MIDAS COMBI

[Bill Riichardson]

My combi has been installed for 8 years, Has been serviced every year since and never been any prob until now. Central heating works fine but hot water giving problems, it comes on fine when hot water tap turned on, runs hot for approx 1 min then gas goes off and water runs cold, if left running it will come on again after a few mins but again swithches the gas off. you can hear boiler close down. Have had main circuit board changed, sensors and thermostat changed,pump changed with no avail. The engineer carrying out the repair is starting to run out of ideas. I suggested that boiler may be sludged up or have deposits as I live in hard water area and was overheating, this was poo pooed, I dont suppose they like an amatuer telling them in case I am correct. I suugested a complete new boiler but they insist it can be fixed as boiler is in very good condition. This is costing a bloody fortune £275 to date and still no further forward. Oh I tell a lie there,I now have no hot water at all.They are coming back tomorrow for a 3rd attempt. HELP before I have to remortgage to repair this boiler.

[geoff]

In message , Bill Riichardson writes

Do either you or your boiler bod have the boiler manual?

The LED sequence is very useful in isolating the cause of problems

If you don't, I can make a copy of the relevant bits, but I would need to know which main board you have. There are two, the 404S656 (which has

6 LEDs in a line) and the 404C147 (which has the LEDs dotted around the board).

If you want to ring me at work, I'll see what I can do. Contact details are on the website -

[Jason N Beck]

wow your lucky 8 circuit boards and the whole thing rebuilt about 4 times. in the end british gas said they would not do any more work on it, same problems as you.

[Ed Sirett]

Almost certainly you need to descale the secondary heat exhcnager. The boiler just can't get enough heat into the HW through the chalk and so shuts down.

If you have a HW temperture control you might be able to turn it down and get the boiler to make a much smaller quantitiy of HW without cycling the flame on and off.

Incidently since the CH works fine there was never any good reason to change the pump, was there? Though sensors, thermostats and PCBs were all _possibilities_ which have now been eliminated.

If possible try to get the temperature of the primary water measured just before the gas cuts - this should be around 80C +.

[geoff]

Since he's probably left uk.d-i-y now

it was the air flow sensor (which is two temperature dependent resistors in a housing)

The fitter battled on, determined to fix the problem and didn't charge above the quoted price to fix it, despite spending well over a day getting it sorted. Well done that man