Myson Apollo Boiler cycling.

[conny]

In rented property so landlord is responsible for repair but just looking for some ideas.

Its a Myson Apollo though not sure if its 15/30, 30/50 0r 40/50.
Fitter came out today and fitted a new thermocouple as boiler pilot would not ignite. Seemed fine when he left and rads were beginning to warm up but didn't get hot. Then noticed boiler was igniting for 10 seconds then switching off for 15 seconds before re-igniting for another 10 seconds. Turned room thermostat in the hall up to 25 from 18 but it didn't make a difference.

Fitter said the three port valve isn't working correctly but he didn't have one with him today to change it. This was after we told him some of the rads got hot when we just had the water on, (this was before the thermocouple problem).

So, basically, can anyone give me any ideas why it is cycling and is it a big job to rectify. Calling the fitter back to do it as I haven't a clue.
If its any significance he said he had to fit a thermocouple with a 'cut-out' in it as that is what was fitted previously.

 

[Boilerman2]

Has he left the temeperature switch on the "LOW" setting, Apollos nearly always have to be set to the "HIGH" position to be of any use! otherwise it sounds like a circulation ptoblem due to air, three port valve or pump, as you already know about an issue with the 3 port, I would get the guy back it certainly has nothing to do with the thermocouple

 

[conny]

Hi Boilerman. Thank you!!! Just spotted the rocker switch was set to low. Flicked to high and it seems to be staying on. Fitter was due to come back tomorrow after 3.00pm so will keep an eye on it and hope its sorted.

He came out originally because there was nothing working at all and I suspected the thermocouple. After he changed it yesterday the boiler came on but after he left it started cycling. He still has the valve to replace but so long as we can get heating for now I'll be happy to wait for him to do the valve.

Once again, thank you for your advice.