Weird boiler problem!

snowleopard61

I have a Remeha combi boiler, installed about 3½ years ago. The heating engineer who installed it has never been able to resolve the following problem, which arose towards the end of the second winter, and I've given up bothering him about it.

The thermostat (the brand is Salus and we have tried both a wireless and a wired version; in fact two wireless ones in case the first was faulty) appears to be working, in that it shows a 'flame' symbol when the temperature for the heating is above the room temperature, but the heating can come on when the thermostat shows it should be off, and vice versa. As a result I can't risk leaving the heating on a timed setting because it could come on all day when I'm at work, or all night, and waste money.

I could deal with having to switch it on and off manually all the time if that's what it takes, but although the 'off' setting reliably keeps it off, sometimes I can't get it going when I switch it on, and sometimes it starts and then switches off (this is not just the thermostat kicking in; the radiators will be going cold as well). Sometimes, but not always, running the hot tap will kick-start it. This morning I tried that several times over the space of an hour, gave up, and then half an hour later had another go and it just started easily. Ironically it sometimes seems to be hardest to start when the weather is coldest, or in the mornings.

Is there anyone out there who can suggest what may be wrong with it? As the original heating engineer was Gas Safe registered and (so far as I could make out) competent enough, given that he had resolved any problems I had with the previous boiler until it was just past economic repair, I'm reluctant to throw good money after bad by calling in someone else, and can ill afford to. The heating engineer was completely stumped by it, even though he had asked others in the trade. I'd be extremely grateful if anyone could help.

southcoastrgi

does the reciever have a red power light & a green light when the heating is on & the stat is calling for heat ? the room stat should be volt free (24v) not 240v & it should be connected to X9 7&8

snowleopard61

Thanks for replying. The boiler has two red lights when the heating is on (and/or when the hot water is running), one red light when it isn't.

I'm sorry if this sounds clueless but I don't understand the second bit about the voltage etc. at all; I'm not very technical!

southcoastrgi

sorry i was talking about the reciever for the room stat if it was still a wireless one, i always change the display on the front of the boiler so you can see what is going on, the way he has left it means you have one dot when it's not working & two dots when it's running, if the display is changed to be on then you can see what is happening, if you feel confident to press the buttons on the front of the boiler i can tell you how to do it

snowleopard61

Thanks again - if you can tell me what to do I'll give it a go. I'm not at home at the moment and probably can't do it tonight, but I'll keep the instructions and try when I can. Very kind.

gas4you

Has your boiler got the pressure sensor fitted for monitoring the system pressure?

These were fitted as an after thought and as such if it cuts in there will be no fault code and the boiler just sits there doing nothing. These are just wired into X9 across terminals 7&8.

I have found that some of the early ones cut the boiler out at just under 1 bar, which is too high IMO.

Room stat/receiver doesn't have to be 24v, it can be 240v but then wired into X2. I prefer this now this new pressure sensor has been fitted as described above.

Also, very often when weird and unexplained faults occur on this boiler, the first thing I do is replace the ntc's as a test, although I have the luxury of always carrying spares on the van.

These were notoriously unreliable on earlier versions, throwing up strange errors and operating occurrences.

snowleopard61

Thank you - there is a pressure gauge in the form of a dial (I hope this is what you mean?) and the heating engineer used to keep the pressure at approximately the 'ten to the hour' position. I know how to increase the pressure so if it drops at all I raise it to that level, but that doesn't seem to be an issue very often and doesn't seem to help particularly.

I don't understand the bit about the voltage but my lovely bf (who understands electrics pretty well but isn't a heating engineer) probably will, so I'll quote it to him.

Sorry if I'm being a bit dim but what are ntc's?!

snowleopard61

Another thing that sometimes kick-starts it, when it won't come on when manually switched on, is to turn the thermostat down very low,so that the flame symbol goes off, and then up again to the required temperature so that it comes on again. This often but not always works to turn the boiler on, though it doesn't always stay on.

ziggyman99

Ntc's are temperature sensors. They are really called thermistors but a lot of engineers call them NTC's, short for negative temperature coefficient thermistor. There you go.

gas4you

No the pressure sensor is a 'switch' fitted to the pipe work inside the boiler at the back behind the fan assembly,

The exterior gauge is a different thing altogether.