sime friendly problems

i have a sime friendly combi boiler and i keep getting 2 problems with it.
1. the pilot light will go out every now and then, sometimes once a week sometimes two or more times a day, what could this be?
2. If i turn the hw upto full temp on the dial the water will run hot , in shower/bath, then run cool for a while. i turned up the incoming water flow to try to stop it overheating and cutting out while running full temp but the boiler cannot heat the water quick enough. im left with turning the temp down to about 3/4 full and slower incoming water. this stops the boiler from over heating then restarting again but dosnt give really hot water, what could be the problem?
sorry for long questions, any help gratefully recieved
nearly forgot, i also have 1 nearly cold radiator in my back bedroom. the bathroom fills up first then the back room then the 2 front bedrooms. the front 2 and bathroom rads are very hot but the bb rad dosent warm up. ive bled the air out and the valves are turned to hot. ive tried turning the bathroom rad down to put the water into the bb rad but still no better, any thing else to try?

Pilot light probably needs new TC ( a CORGI job ).

Poor DHW performance may be caused by dirt in the secondary heat exchanger or possibly a faulty sensor or incorrectly set gas valce.

Tony

the dirt would be removed with a service? ive had a circuit board replaced because it had burnt out. would it need new tc and gas valve? tc=thermocouple. would this help with dhw?

the dirt would be removed with a service?

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No!

tc=thermocouple.

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yes

would this help with dhw?

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No!

GV may need adjusting - but dirt inside heat exchanger more likely

would a thermister sort out the hw problems?
and how would the dirt be removed?
how is the gas valve adjusted or is it just replaced? roughly how much should i be looking at paying for this work to be done?

In London we would charge a fixed diagnostic fee of £84. Supply and fit a new TC would be £8, a sensor £13 ( unlikely to be the problem ), remove and clean the secondary HE £48 ( most likely to be the problem ).

If there is a lot of dirt in the system merely cleaning the HE will only postpone the reoccurance and power flushing would be the only way to guaranty the system in the future.

Prices fairly obviously include a service check as otherwise we could not diagnose the fault(s).

Tony