RAVENHEAT CSI SYSTEM BOILER OVERHEATING

[smida]

On several occasions during this cold weather I have been woken by a banging noise from my boiler and also steam coming out of the air vent.

After several nights of this I have done a bit of detective work and can deduce the following.

The central heating isn't calling for heat but the hot water is.
The pump is running.
There is enough pressure in the boiler.
It normally happens about 4-5 hours after the heating is switched off after I have gone to bed.

When the boiler is overheating and venting, if I make the central heating call for heat the water is pumped around the heating circuit and so the boiler stops overheating and behaves itself.

I thought the pump may be sticking, a plumber friend of mine rang Ravenheat and they said the same, as luck would have it I had a replacement pump and swapped it out to no avail.
(i have since checked and the pump is running when it is overheating)

The boiler is connected to an Ariston pressurised hot water cylinder which has an energise to open valve fitted on the hot water supply pipe from the boiler. This gets it's signal via a relay from the boiler.

The top and bottom of it seems to be that when the hot water only is calling for heat there is some form of restriction in the pipe, either the mid port valve or the valve local to the pressurised cylinder. Thus the water can't circulate and hence the boiler "boils". Now for the strange bit, it only ever happens in the early hours of the morning, once I call for heat on the heating and the boiler stops "boiling" I can turn back to hot water setting and it works fine. During the day it works fine also, although the heating will be coming on and off with regular frequency as the house is occupied.

I am somewhat puzzled and would appreciate any assistance.

Thanks

 

[Happyplumber]

This sounds very much like a controls problem,was your boiler fitted by G3 certified installer and is the bypass fitted correctly?

Has the system been wired up correctly?

 

[smida]

Thanks for response, but the boiler has been working fine for the last 20 months. At first i wondered if the mid port valve was somehow freezing as it is in the garage and it was minus 12 the other night but last night wasn't that cold and it did it again.

 

[transam]

Has the system got a by-pass fitted ??? Sorry did not see Happy plumbers post !

 

[smida]

Bypass is fitted.

As it appears that this fault only happens when the system has had chance to cool for several hours and then only when DHW calls for heat, could there be some fault with a temperature sender on the DHW side of the boiler.

As I mentioned before, once you flick the room stat to call for heat you can turn it back just to DHW and all is fine.

 

[Happyplumber]

I see you have not answered my question about this system being fitted by qualified person ,you need someone to come in and check the controls and sort out the problems,i think from the choice of boiler and cylinder this job has been done on budget and few corners may have been cut

 

[smida]

Apologies for not answering, yes the system was fitted by a qualified person. Initially the whole system was installed about 5-6 years ago. I agree that to purchase a lined cylinder with cathodic protection instead of a stainless steel one was a cost saving. As for the boiler, again cost was a consideration, having built a new extension I needed extra capacity but the Ravenheat was suitable spec. One problem I did find was getting a qualified person who actually fully understood the system boiler and the fact that it needed a relay to operate the valve on the cylinder as that is 240 volt and the boiler signal isn't.

Anyway that aside, the system operated fine until 20 months ago when the boiler sprung a leak and dripped water over the electrics rendering the thing useless. As my wife was expecting a baby the following day I bit the bullet and bought another boiler of the same make and model which allowed a very quick swap over. The same qualified person connected the gas and commisioned the boiler, everything was fine for the following 20 months until just before Christmas. The fact it has had many years of trouble free operation doesn't really point to a latent defect in the installation.
I think I will have to let the whole system go cold this weekend and the try and observe if any valves aren't opening as they should. Unfortunately said qualified person isn't available until next Monday, so if I draw a blank this weekend I will have to get them to have another look at it next week.