Ravenheat RSF 84ET Combi boiler

Hi all,

This is my first post so go easy (and sorry for making it such a long one!) I've been reading loads of postings and found this one of the most useful forums I've ever come across - top stuff!

Anyway, to my questions...

I have an RSF 84ET combi boiler which has a couple of issues. The main one being that when it absolutely buckets down with rain (like it has done all day here in Liverpool!) water seems to be coming into the house via the boiler. I assume it is getting in via the flu as it is filling up the bottom of the combustion chamber and then slowly dripping out below the ignition spark down onto the controls and then subsequently onto my fresh painted wall! Strangely, this happened once last year around this time and has just happened again today - must be global warming or something!

Anyway, I've taken the combustion chamber cover off and dried out as much as I can for now. Now, should the vent on the external wall at the end of the flu have a cover/deflector over it to stop this sort of water ingress as it appears to offer open access to the elements at the moment. Also, should the seal around the combustion chamber let water through - I'd assumed it should be an air-tight/water-tight seal but that obviously isn't the case. Is this a problem?

On to the second "feature" of my boiler... I have what seems to be a common issue with Ravenheat boilers in that I can't get a constant hot water flow from it - instead I get cycles of boiling then cold water every 30 seconds or so. I'd put this down to crap water pressure to our house before now and simply assumed the boiler was getting too hot internally and turning off the burners for a bit. Luckily we have an electric shower to get around it. In the course of sorting out todays leak I've done some more investigation around the DHW supply and now have some interesting results that I'm hoping someone on here can advise me to resolve.

With a hot tap fully open, the boiler appears to go through the correct process to get the water to operating temperature. Then after a bit the burners simply extinguish and the water gradually cools down, then the process starts again and the temperature comes back up. There is no modulation of the gas pressure to control and maintain the water at the supposed 65degrees (the DHW thermostat is set to MAX.) I've just noticed that the DHW thermostat control does not seem to have an effect on the water temperature or indeed the gas burners. If I let the boiler go completely cold and then open a hot tap fully, the water heats up and keeps heating up till it eventually overheats and turns off the burners. If I turn the DHW thermostat control up and down I can hear a relay clicking on and off but this has no effect. It's as if it isn't sending a signal to the gas burners to power down slightly. If I let it run its course the point at which the relay flips gradually moves around the DHW thermostat control, starting at a bout 7o'clock and moving round to about 5o'clock if that makes sense. The relay clicking noise is coming from what is described as the ignition board/modulating gas valve area (which fits in with the problem I'm seeing.)

The manual for the boiler implies it is the DHW thermostat that is kaput but seeing as the relay is switching apparently correctly I'm not convinced this is the problem but have no idea what it is.

Again, sorry for the long post but hopefully I've given enough info to enable someone to help me make either perform what hopefully could be a simple DIY fix or if not help a corgi-man with a decent explanation of the problem.

Thanks in advance,

Gareth.

RE the flue, it should be angled downwards slightly as it leaves to boiler to prevent the rain from entering, have a check.
The seals should be air tight and COULD become dangerous should the exaust outlet of the flue block up.

RE the hot water, first thing to check would be thermistors, does the resistance decrease as temp rises. requires multi meter.

its more likely to be a scale in the HW section of the HE than a modulation problem, if you rule out thermistors

1,Your flue has not been installed correctly. It should slope away from the boiler.

2, I have come across a few with the hot cold water cycle on this model.
Most times it was the hot water thermistor, a couple of times it was the hot water potentiometer.

The fact that you can hear the "clicking" whilst manipulating the hw control knob could mean its something else.

Hard to say without being stood in front of it.

rob884 said:

RE the flue, it should be angled downwards slightly as it leaves to boiler to prevent the rain from entering, have a check.
The seals should be air tight and COULD become dangerous should the exaust outlet of the flue block up.

RE the hot water, first thing to check would be thermistors, does the resistance decrease as temp rises. requires multi meter.

its more likely to be a scale in the HW section of the HE than a modulation problem, if you rule out thermistors

Click to expand...

Hi,

Thanks for the quick response... I'll check the angle of the flue and see what I can do with it - if there is no way I can adjust it now that it has been fitted I'll see about some sort of deflector mounted above it.

I've not checked the thermistors - I'll do so if I can.

Why do you think it is scale in the HW section? The fact I can hear the relay clicking but there is no noticeable adjustment of the gas pressure makes me think it is some sort of control issue. Or would the scale problem directly affect the control systems?

scatmanjohn said:

1,Your flue has not been installed correctly. It should slope away from the boiler.

2, I have come across a few with the hot cold water cycle on this model.
Most times it was the hot water thermistor, a couple of times it was the hot water potentiometer.

The fact that you can hear the "clicking" whilst manipulating the hw control knob could mean its something else.

Hard to say without being stood in front of it.

Click to expand...

D'oh - as both of your replies state, the flu has probably been installed incorrectly. I'm not sure who/when the boiler was fitted as it was in when we bought the house but based on some of the other "features" I'm finding with some aspects of the house's maintenance/DIY it wouldn't surprise me if it had been a bodge job by someone!

Yeah, I've read loads on here about problems with a couple of models in the Ravenheat range cycling through hot/cold - as you say though, the fact my relay is clicking does confuse the issue a bit.

Just to clarify my understanding, the DHW potentiometer is the actual temperature control knob for the water temperature and the thermistor is the temperature sensor on the DHW circuit? Is that correct? Is it possible that the thermistor is knackered and this in turn is sending mixed messages to the gas control valve/pcb?

Any other suggestions?

Thanks.

Ok done some more investigation and it turns out the water coming in was due to some dodgy guttering that had moved - basically there was a downpipe pouring water right on top of the vent for the boiler! Sorted this now.

Anyone got any more suggestions as to the problem with the gas modulation?

Just to clarify my understanding, the DHW potentiometer is the actual temperature control knob for the water temperature and the thermistor is the temperature sensor on the DHW circuit? Is that correct? Is it possible that the thermistor is knackered and this in turn is sending mixed messages to the gas control valve/pcb?

Click to expand...

Yes & Yes

scatmanjohn said:

Just to clarify my understanding, the DHW potentiometer is the actual temperature control knob for the water temperature and the thermistor is the temperature sensor on the DHW circuit? Is that correct? Is it possible that the thermistor is knackered and this in turn is sending mixed messages to the gas control valve/pcb?

Click to expand...

Yes & Yes

Click to expand...

Thanks!

I'll have to do some checking then... Will let you know what happens.