Combi boiler low pressure

[CMS]

Bear with me - this may be a long story/question.
Firstly, boiler is a Ravenheat RSF 100 which is about 2 years old.

Recently we have had a loft extension and had two new radiators added which all worked fine.
Anyway, last week the hot water stopped working properly - ie it ran hot and then cold, then hot, cold etc.

Man came to look and said needed a new thermistor which he fitted. (Imbetween his diagnosis and fix, the pressure dropped to 0.5 bar).

As he had added water to system (to get pressure right), he said there may be air in system in which case bleed the radiators. This was true as the 2 in the loft were cool. I bled them both so they were nice and hot and then noticed the pressure had dropped back to 0.1bar. I added water to get the pressure up to 1bar, but after about 1 hour it dropped back to 0.

Wondered if there was a leak of any sort and discovered water on the ground outside behind the boiler.

Phoned boiler man again to be told probably the safety relief valve and he will come again sometime(!)

Both the heating and hot water are fine now.

My questions are - is this anything to do with new radiators?
Could this new problem be anything that the boiler man did on his first visit?
Does his explanation seem a reasonable one, and if so, what fix is needed?

Thanks.

 

[taydo]

ok im only second guessing here but more than likely he used the pressure relief valve to drain the boiler when he replaced the thermistor. They do tend to be a little tempremental and sometimes leak when used. Most of the time if you turn it in the direction of the arrow a few times so that it thumps home it seats itself again. if not then you will need a new prv.If you do this yourself make sure the system is switched off and cold as the water that shoots out through the wall does so with quite a bit of force.

hope this helps

Best regards Brian

 

[CMS]

Thanks Brian,
Also, as mentioned the two radiators in the loft did have air in them. Having bled them and then being ok and hot (this morning), one of them is all cold at the top again now. I have just tried to bleed it and got the usual hissing sound.
As a complete novice, how come it needs more bleeding?

Thanks

 

[boilerbeasty]

They need bleeding over a day or two with the heating running during that time. There's not one big air bubble which gets pushed around to the top of a radiator until you let it out. Instead there will be lots of smaller ones, and a lot of dissolved gas in the water.

I've drained my system out through the prv, but ended up having to flush lots of clean water (straight through the filling loop and then out through the prc) to make sure the seal was clean and it would reseat. If you have a tiny bit of crud which gets stuck, it can leak very slightly and drip. Better to use the draincock.