Grandee Combi Oil Boiler

[poorpostman]

Hi forgive me if I have posted in the wrong place i'am a newbie
we have just purchased a property fitted with a 10 year old Grandee oil combi boiler which still works fine on central heating but is terrible on hot water we can not have a shower without the water running cold after 40 or so seconds on looking at the boiler I noticed first that the boiler does not ignite when the hot water tap is turned on and second that the circulation pump turns off when DHW is selected from the programmer is this correct?

Thanks Dave

 

[oilhead]

Possible problems with this boiler are flow switch, diverter valve or thermostatic mixing valve.
When selecting hot water on programmer, the pump will stop because there is no slave tank to heat up. When a tap is turned on, the flow switch should turn on pump, burner, and operate diverter valve so that water is sent through the heat exchanger. If the mixing valve is kaput, then if the boiler is up to temperature, the burner will not ignite.
Best to call in an experienced technician.

 

[Boilerman2]

On the Wall hung combi some of them are fitted with a pump that runs constantly! (TBH Grandee are Horrendous and I would replace it as soon as funds allow - you won't regret this advice!!

 

[poorpostman]

Thank you for your quick responses I had a chat with a couple of our romec engineers today they recommended as a test that I disconnect the boilers wiring to the pump taking care to insulate the wires after diconnection, then connect a new lead to the pump via a 5amp fused plug as this would help eliminate some of the likely causes and it has pretty much done so.

With the pump running continuous I am able to to switch between heating and hot water from the programmer so I presume this would mean the diverter valve is OK,

I am also able to get lashings of hot water at a steady temperature so I presume this indicates the thermostatic mixer valve is OK,

The only thing that seems not to function correctly is the flow switch as the boiler will still not ignite when hot tap is turned on, could this be my problem.

Thanks

Dave

 

[Agile]

Hi forgive me if I have posted in the wrong place

Thanks Dave

I dont expect YOU to post in the wrong place!

But I do get at least a letter a week wrongly delivered to me.

My car tax disk has not arrived either!

Back to your boiler, I expect the DHW flow switch is failed from what you say.

Tony

SW1A 1AA

 

[poorpostman]

Crikey I would have never guessed that residents of SW1A 1AA would be posting on DIYnot! but while I have your attention would there be any chance of a OBE or Knighthood going to a postman with sore feet and a dodgy back at the next honours giveaway? but seriously thanks for the input it seems the boiler will be an easier fix then I had first feared,

Thanks
Dave or maybe Sir Dave

 

[oilhead]

On the Wall hung combi some of them are fitted with a pump that runs constantly! (TBH Grandee are Horrendous and I would replace it as soon as funds allow - you won't regret this advice!!

Which boilers run the pump continuously, except Camrays where the diverter head is knac*****d? Once up to temperature, either heatstore boilers or those that use the main heat exchanger should cut the pump off when there is no demand from a thermostat.
Don't find Grandees too bad, but like all oil combis, you need to keep an eye on leaking joints.

 

[Tibbot]

The wall mounted ones I've fitted and worked on definately had the pump working all the time there is external power. The only way to stop it is to cut HW pre-heat demand with a 2 ch timer.

 

[cornishgas]

I realise this is after the event but for anyone that picks up this thread the Grandee combis I've seen continuously pump through the plate heat exchanger to ensure there is hot water on demand because there is no slave tank. There is no voltage to the flow switch on hot water only but there is when calling for central heating. If the central heating is on and you turn on a hot tap the flow switch kills the voltage and returns the 3-port valve to hot water i.e. It doesn't work like a Heatslave!

 

[dcawkwell]

Most likely flow switch. Which is easily tested.
These are a bitch to work on and removing the flow switch will probably make all the joints leak and need new washers on.
What idiot thought of that piping arrangement. I could do better.

When tap is turned on the boiler should fire.

 

[Boilerman2]

Three years after this post first appeared we are still discussing the Grandee!!

The circ pump runs 24/7 unless a 2 channel clock is fitted, but then there will be no hot water out of hours - which is not really what a Combi is about!

The boiler stat controls the burner, and when the flow switch detects an open tap it overides the boiler stat bringing the burner on regardless of boiler temperature, the hydronic layout is terrible, the HE versions are worse, there is nothing good that I can think of to say about these models!

 

[leakydave]

I was called to one of these combis recently. The flow switch was leaking. A replacement was of a different design so I had to cut the internal flanges off the 'tap connector' style coupler and file flat to get the new one to fit... as advised by Grandee themselves.

Then when changed the boiler was heating the radiators with the heating off. Diverter valve head stuck in one position with power off or on and no movement in the lever. Replaced the diverter valve and now hot water but no heating!

I will get an electrician friend to check the output from the time clock on Heating Side.

Any other suggestions?