Grant Vortex Oil Boiler fault, CH stops when HW is running?

[Nihad]

Hi all

We have Grant boiler
It never bothered us before but i’m curious to know whether this is a fault or normal for Grant boiler central heating to stop when the hot tab is running?
Also when the hot tab is off then it takes CH 5-10 mins to come back on

Any suggestions much appreciated

Thanks

 

[RandomGrinch]

Is it a combi?
It is normal for a combi!

 

[Nihad]

Is it a combi?
It is normal for a combi!

Combi yes.

 

[RandomGrinch]

Combi yes.

As above, a combi can only supply heat to hot water, or heating; not both together.
If you are used to having a separate hot water tank, it may take some getting used to, but it isn't a big deal.
I.e. to get around the limitations; putting the heating on for 20 minutes before having a shower, would be a good idea, for a comfortable bathroom temperature.

 

[ericmark]

I had not realised it turned the CH off, in the main oil fired central heating combi boilers don't give instant heat like gas ones, as in the main they don't modulate, so there is a water store inside the boiler, which has priority.

 

[RandomGrinch]

I had not realised it turned the CH off, in the main oil fired central heating combi boilers don't give instant heat like gas ones, as in the main they don't modulate, so there is a water store inside the boiler, which has priority.

Good point Eric. Apologies, my post was a little simplistic - the transition between firing for heating or HW supply may be more, or less noticeable, depending on the size of the thermal store.
The diverter valve will always give hot water priority.

Although, I should really have asked the question - has the boiler always behaved this way?

 

[Exedon]

Normal behaviour its how it works.
There is no diverter valve on a Grant combi uses 2 pumps.
On hot water demand flow switch operates hot water pump starts, when temperature of heat store drops burner fires.
When flow switch closes pump/burner will continue until heat store thermistors are satisfied.
Burner will shut down pump continue to run for around a minute. After that is there is a heating demand heating pump and burner will operate.

 

[Johntheo5]

Normal behaviour its how it works.
There is no diverter valve on a Grant combi uses 2 pumps.
On hot water demand flow switch operates hot water pump starts, when temperature of heat store drops burner fires.
When flow switch closes pump/burner will continue until heat store thermistors are satisfied.
Burner will shut down pump continue to run for around a minute. After that is there is a heating demand heating pump and burner will operate.

Any idea where the temperature sensor is (and its dT) to fire the boiler when the store temperature drops, even if the 32L? store is completely exhausted and down to 20C then even a 26kw combi should restore this to 80C in 5 minutes max and a 36kw combi in < 4 minutes. If its taking 10 minutes to change back to CH then seems a bit on the long side even for (if ) a 26kw combi but then again, maybe not, since it must heat the boiler contents as well.

 

[RandomGrinch]

store is completely exhausted and down to 20C then even a 26kw combi should restore this to 80C in 5 minutes max

Yes, although..

Also when the hot tab is off then it takes CH 5-10 mins to come back on

Is a little vague.
For instance, if a full bath were drawn, there may be a noticeable lag before the full heat output was restored to the rads?

 

[ericmark]

Just glad mine is not a combi, it just heats a cylinder of hot water.

 

[Johntheo5]

Oil fired combis by their very nature (non modulating) require a store otherwise the DHW would be running hot and cold at any demand lower than the boiler output, because the boiler would be cycling on and off, if there is a big demand and all the store is used then a bit difficlt to calculate what is the maximum flowrate available without the store increasing in temp until the DHW demand is finished.
A 26kw gas fired combi boiler will give a DHW flowrate of 12.42LPM from mains at 10C to DHW at 40C. Not sure if the oil fired will do the same (store depleted and no reheating) but probably, the total primary contents are the boiler HEX contentsof say 20L + the store contents of 32L, total 52L, so if the DHW demand decreaseed to say 1/2 of that (thermally) of the boiler output then the store will start reheating and might be almost fully recharged when the DHW demand finishes, so, in those circumstances, should change back to CH with very little delay. If the store is depleted when the DHW demand ceases then the boiler must reheat 50L of water which can definitely take up to 10 minutes, so the 5 to 10 minute delay is probably a true reflection of, as stated above, "Normal behaviour its how it works."

 

[Exedon]

Any idea where the temperature sensor is (and its dT)

It has 2 thermistors on heat store control and high limit connected strait to the board.
To be honest don't know dT used but I've a meeting in week with Grant technical rep will ask the question.