Radiators Inflated Like a Balloon - Dodgy PRV?

[Rm73]

Hello all,

I'm a fitter with a question is regarding a PRV.

We fitted a new Worcester Compact 30si for a family in early Feb 2014. Been working OK ever since, save for customer noticing a long delay in the heating kicking back in if someone runs a tap etc so after I visited to check the external controls etc I called Bosch and booked an engineer visit. PCB I thought.

BTW: I've been to this place about 3 times following installation for other unrelated things and as always I checked the boiler quickly to make sure it looked ok (pressure, temperatures etc) - always fine.

Worcester sent someone who (apparently) reduced / removed the heating delay facility on the board, she also changed the MT10 internal timer and then said she thought my wireless room stat was also somehow at fault (despite the stat being operationsl). God knows what else she did to the boiler but it was left working and away she went. The customers summary of the visit smacked of an engineer who was out of her depth and just carrying out random work...

Anyway, approx 34 hours later the customer heard banging, water coming through living room ceiling, noticed two approx 20 year old steel rads had swollen up like balloons ready to pop! Turned off system.

When I got there the boiler pressure was at 3 bar, PRV dripping but only slightly. External screwdriver-slot type Filling loop left very slightly open. I had a think about it all and I guess that if the Worcester engineer had refilled, and effectively overpressurised to +3 bar at night when street mains pressure rises then the expansion vessel becomes useless, however the PRV should have kicked in and done its job. I twisted the PRV and when used manually its fine. What I could not test at the time was its calibration (whether it activates properly at over 3 bar) as I had no way of putting +3 bar in at that time of day.

I think that a faulty spring in the PRV could have led to this. If spring is too stiff then maybe it would not activate? Its def not blocked as I managed to open it by hand.

I saw a similar thread here from 2008:

//www.diynot.com/forums/viewtopic.php?t=134919&start=0#.Uyd8nBHeVWE.email

Lots of differing opinions there...Rads on my customers job look the same as in above thread

 

[Rm73]

I too have experienced this phenomenon. The rad was perfectly round. System was conventional boiler with pumped ch and gravity hw. Rad was appx 5 years old. Annually serviced and fernox treated Thermostatic valves fitted on all other radiators on system apart from the one blown up. I was out at work when it happened. Step daughter was home and described the noise as each weld popped as like a explosion. The rad had zero corrosion and was in excellent condition before hand. No exaggeration the rad was nearly perfectly globe shaped. My dad worked at college and showed plumbing lecturers who was astonished. The system was tested before the replacement rad fitted Nothing was found to be faulty. Working fine still today I am a metallurgist and worked in a laboratory. Tested everything possible and nothing remotely could explain how the pressure could get so high. Why any valve did not release any of the pressure before the point of swelling is reached. What stopped the flow of ch water in the circuit No blockage ever found. Why it never happened before or after. The pressure needed to do this to the radiator must be incredible much more than a ch pump and a small one at that could possibly achieve. Complete mystery Just came to me that I should search for other people who have seen this The Internet was not about when my rad blew. Scary