Ravenheat CSI 150 versus underfloor heating nightmare

Im posting this in the hope of help/inspiration and to vent some steam (no pun intended!)
I have a Raveheat CSI 150 fitted about 4 years ago by my gas safe chap. It feeds the domestic hot water and an underfloor heating system on 2 floors. I had some initial boiler problems but follwoing these everything has run ok for 4 years. The property is rented out and when i got new tennants I paid for the underfloor heating installers maintenance partner to come to site, service the system and set all the controls up to suit the new tennant. the following day the boiler locked out showing error code 04 which is apparently overheat (set at +80 deg C I believe). I got the underfloor guys back out but they could find no problem and offer no suggestion why the error could happen. over a period from this date error code 04 has constantly re-ocurred. Ravenheat have blamed the underflor heating system consistently but cannot offer an explanation as to how the underfloor could cause the error. Ravenheat and the underfloor guys have been on site about half a dozen times and the problem persists. ravenheat have replaced all the sensors/thermistors twice, the board twice and the wiring between, and have flushed the heat exchanger. for my part i have replaced the auto bypass valve between the boiler flow/return and the underfloor system. the underfloor is a Velta system and comprises a blending station including 3 port valve, grundfoss pump, some electronics, miles of pipe and two manifolds with solenoid valves. as best i understand error code 04 menas that water is getting back to the boiler at a higher temp than its trip point (+80?). however the boiler output is only set at +45 as this is all the underfloor needs. regardless of any malfunction with the underfloor system how can water leave the boiler at 45 and arrive back at above 80? Ths has been going on for 8 months now and as its summer its less of an issue but winter will cause the issue to arise again. we still get the boiler locking out on error 04 now when the heating isnt running but the DHW is so this also convinces me its a boiler fault. Ive written to Ravenheat asking them to explain how the underfloor heating system can cause the problem but the best they can offer is that they've replaced all the parts associated with generating error code 04 so it cant be the boiler. Im looking at having to rip out and bin a 4 year old boiler without any understanding of what the problem really is and as a comnsumer im stuck between the boiler manufacturer and the underfloor manufacturer who point at each other. any ideas/thoughts/suggestions or experince with ravenheat error code 04????
cheers for reading my rambling post!

turn the boiler back up to 70c, the blending valve on the underfloor heating brings it back down to 45c, might be worth checking the pump as this is the first suspect on overheat lockouts,

any idea what the maintenance guy adjusted on his first visit ?

one more question is it cutting out when you run the hot water as well ?

picasso said:

turn the boiler back up to 70c, the blending valve on the underfloor heating brings it back down to 45c, might be worth checking the pump as this is the first suspect on overheat lockouts,

any idea what the maintenance guy adjusted on his first visit ?

one more question is it cutting out when you run the hot water as well ?

Click to expand...

many thanks for the reply. weve had the boiler output set at pretty much every possible output temp but to no avail. the pump is running ok on the underfloor blending unit, i cant vouch for the one in the boiler but im assuming it must have been checked as ravenheat have had the boiler in bits half a dozen times (i know thats no gurantee!) Im not sure what was adjusted on the floor system maintenance vist but theres not a vast amount of parameters that can be messed with other than temp set points and times etc. One thing I cant understand (not being a mech engineer or plumber) is regardless of what the underfloor heating does, if the boiler is only set to output 45 deg how can it get water back any hotter than this even if its going stratght through the by pass to the boiler return? is there a possibility that although its set for 45 its actually producing water hotter than this? if so then the heating system blend valve would be shut and the boiler output would go straight through the by-pass. I understand that the error codes are still happening now when the heating isnt calling for heat and only the DHW is running.
cheers

As its happening on hot water as well as central heating I would say pump or blocked main heat exchanger.

04 = an overheat stat lock out

they use a standard Giacomo heat exc same as many other manus , there are only 3 stats on the boiler, overheat , ch & hw ??? & u say they have all been changed ? trigger temp for the OH stat seems to be 95 degs C from what I can see (maybe ?)

As has been suggested ,by piccasso there would appear to be a circulation problem ?

If boiler is locking out during HW demand, then the problem is within the boiler. During HW mode, heated ( dirty radiator) water does not leave the boiler. Internal pump keeps the water circulating within the boiler and controls keep an eye on the burner so things do not get too hot and give you code 04

Easiest way to locate circulation problems is by means of dual clamp thermometer

Exactly!

If I encountered this problem, I would not bother much about further diagnosis and would just chemically treat the boiler on its own. Probably with citric acid.

Tony

thanks for all the replies. Ravenheat stripped out a heat exchanger which im guessing was the DHW - it was a rectangular metal box with sort of corrugated sides. the engineer flushed it out but it had no debris in. I think i might get my gas-safe chap to flush the boiler, treat it and then ive got an infra red thermometer so i will check the output temperatures (pipework surface) just for peace of mind to see if it is outputting water above the set point, and we can check the pump is running.

cheers

You need a contact thermometer to get meaningful readings.

Tony

managed to get underfloor heating manufacturer to send their (very knowledgeable) engineer to have a look. He has confirmed no fault with undefloor heating. the blending station has probes that sit within the water flow; we ran the system for maybe half an hour with the boiler CH output wound up to maximum (showing 74 on the boiler display) and it never got hotter than 45 according to the underfloor heating probes.
all I can assume is that for some reason the boiler miss-reads the flow and return temps and as a result locks out on overheat. its clear the flow temp wasnt 74 deg as i could put my hand on the pipe.
given that all the sensors, the PCB and the interconnecting wires have been swaped in the boiler im begging to conclude that the boiler is either haunted or just a heap of the proverbial.
I think i may just have to bite the bullet and buy a new boiler.