Central Heating blowing hot and cold

[answer_raj]

Why are the radiators to my gas central heating hot one minute and then completely cold within 10 minutes. Given 1/2 to 1 hour they are hot again and then cold. This happens to all the radiators in the house.

[trendypaul]

I can't think of a reasonable reason for this to happen however I have only been plumbing for just over a year. We have covered many problems but nothing like this.  I think the best solution is to get a plumber in, especially as it's probably an issue with your boiler.

[fibifooz]

It sound as if you have air in your system. You need to bleed your radiators probably just the highest radiator on the system.

[answer_raj]

Thanks for the responses.  I've tried bleeding all the radiators, have also drained the system and put in some sludge remover and drained and drained that out as well - managed to remove some sludge but there wasn't as much as I thought there would be.

[FTVS]

Could it be the thermostat being over sensitve? Does the boiler turn itself off like it thinks it has reached the proper temperature and then turn on again when it detects the house getting colder?

[answer_raj]

I've had a central heating engineer look at it, he seems to think it's the air pressure switch on the boiler - will see what happens when that is changed.

[landie]

Check where your thermostat is situated. If it's too close to a source of heat it will activate earlier than if its remote from such heat sources.

[answer_raj]

You were right, it is an issue with the boiler.  Turns out it was the gas valve.