Grant Combi-Boiler problem

fsa

Hi all,

We bought a house in July this year, and the seller had the boiler serviced before we moved in, replacing the fuel pump, photo cell and nozzle. The system was only installed in 2008, so it's relatively new.

Anyway, the central heating and hot water seemed to be working fine - heats up very quickly etc. Anyway, its only in the last few weeks (as it's turned colder) and we've put the heating on that we've noticed the following;

1. We can only have the central heating or hot water on, not both at once - if the CH is on, the hot water is luke warm at best
2. Because of (1) I set the timer so the CH comes on early for half an hour, then it switches off and the HW comes on for showers. In the evening the opposite happens - HW first then the CH in the late evening.
3. Despite (2), the CH in the evening will come on, get hot for a variable time (30 mins-a couple of hours), then will go off and not come on again. The only way to make it come on again is to switch the timer onto "off", then back onto timed, which seems to sort of reset it and then it'll fire up again.
4. This doesn't seem to have anything to do with the thermostat - which is a wireless Drayton Digistat module - which will still have the flame symbol (indicating it's requesting the heating to go on). when the heating goes off.

Does anyone have any idea what's going on here? The problem doesn't seem to be the boiler itself, as it fires up without any problem (no stuttering, firing then stopping etc), but something to do with how its told to come on.

Any help gratefully received!

Ionkontrol

Make and model?

keystone

Ionkontrol wrote: »

Make and model?

Probably a Grant? Seriously though although model is a good plan it does sound like a controls issue so a description of the total system configuration would be even better than just the boiler model details on its own.

The first person to say RGI gets a slap by the way.

OP I doubt its a combi although it will inevitably be a condensing boiler but not all condensing boilers are combis. Your 1. points to a problem with a motorised valve so please can we get that system configuration data.

Cheers

diywhynot

OP: model of oil boiler?

keystone

diywhynot wrote: »

OP: model of oil boiler?

Spoilsport. Bet you are a riot at parties.

Cheers

fsa

1. Boiler is a Grant floor-standing Combi 90 U3
2. Burner is Rillo RDB PJ Type
3. Programmer is a Drayton Lifestyle Dual channel LP522
4. Thermostat is a Drayton Digistat+RF RF601
5. Sealed system with pressure OK at just under 1 bar cold

Hope thats all thats needed for some insights - thanks!

diywhynot

A combi can't provide heating and hot water at the same time. If your boiler is a Grant oil combi 90 V3 have a look at the manual here.

fsa

OK, that's good to know! At least that means there's nothing fundamentally wrong with it.

Now I just need to address the lack of hot water or CH after a time when on...any ideas on this?

spannerzone

My outdoor Grant combi oil boiler (installed 2010) seems to cope quite well with switching between hot water and C/H - if the radiators are warming up and I turn on hot tap then it gets hot tap water pretty quick (almost instant) and even if running a long shower it doesn't really seem to reduce radiator heat very much at all.

Whether it's down to house size, rooms, bathrooms etc I don't know (there's just 2 of us in smallish house so lowish requirements)

keystone

fsa wrote: »

Boiler is a Grant floor-standing Combi 90 U3

Well now I've learned something today. Didn't know they made combis, thought it was just system boilers - perhaps I should have looked it up.

fsa wrote: »

We can only have the central heating or hot water on, not both at once - if the CH is on, the hot water is luke warm at best

As DYN has said combis only work CH or DHW not both together and DHW has priority. That is to say that even when the heating is on if a tap is opened and DHW called for the diverter valve switches to DHW to give hot water and the CH just ticks over without any additional heat being pumped in until the tap is turned off again. The fact that when heating is on you only get lukewarm DHW suggests that you have a problem with the diverter valve and its not operating properly. Thats either a problem with the valve itself or as you rightly suggest what its being told to do.

Cheers

fsa

Another development this morning - after providing some hot water, the system seems to have stopped completely, and when the programmer is switched to off for both HW & CH and then back onto ON, you hear the burner start and then stop almost immeiately. No lockout light is appearing on the burner and I checked the oil supply is fine.

This has happened before and was rectified by resetting the wireless remote and SCR units, but this doesn't seem to be working this time!

HELP!!!