Running Combi boiler without rads

[sharpspark]

Is it possible to run a combi boiler without the radiators so that we can use it for hot water whilst all the rads are being installed at a later date. I assume this would be done by linking the flow and return pipes together and having the heating demand switched off. The boiler has an internal bypass (Halstead Finest Platinum). I know there will be cleaning and corrosion inhibiting to be done again.

 

[DP]

Boiler may need to dump heat at the end of HW demand. Stubs of pipes and cross link at the service valves may not be sufficient resulting in long periods of boiler over-run. Internal bypass is for pump protection only.

 

[sharpspark]

How about a few metres of 22mm pipe?

 

[billy bob]

It might work if you fitted some pipework and one rad close to the boiler, temporary, but you would have to fill the heating side ie the pipe and the one rad, as it is this water that heats the hot water

 

[sharpspark]

Thanks, yes I know I've got to fill/commision the heating side as well.

 

[Bahco]

I had a combi boiler fitted by a corgi engineer and I fitted the rads etc myself at a later date.
He left the boiler functioning on hot water only by turning off the flow and return at the isolating valves on the boiler and it worked fine.
I commissioned the rest myself and repressurised after turning on both the flow and return.
I am surprised that nobody else has mentioned this, perhaps I was badly advised

 

[billy bob]

Bahco

I cannot see how that is possible, the hot water in a combi is heated indirectly via a heat exchanger, the water that heats the heat exchanger is the central heating water, there has to be some kind of circuit for the pump to circulate the water around the heat exchanger to allow it to collect heat from the boiler heat exchanger and pass this to the hot water via the hot water heat exchanger, can you explain how yours worked, what boiler was it

 

[Bahco]

It is a Valliant Turbomax and I can assure you the domestic hot water works with the flow and return valves turned off.I don't pretend to be a boiler engineer and will welcome any comments about this

 

[billy bob]

I am a heating engineer if you must know, I don't pretend to be anything else, the way you say that your heating engineer fitted the boiler and you did the heating at a later date would not work, as I have said before the hot water side will not work unless the heating side is full of water.

 

[AlanE]

Turbomax has pump overrun to dissipate heat in heat exchanger following operation for DHW.

With no path in heating system circuit there is no place for this heat to be dissipated and I would have expected the over heat stat to operate.

Alan

 

[namsag]

Any combi with a built in filling loop can run without the need for the heating side being either connected or full of water so Bahco could quite possibly have been able to run his without having the heating connected and boiler isolating valves turned off.. Dependent on how long it was run for and how hot it got would then dictate wether built in by-pass would disapate heat without over heat stat tripping and as a lot are self resetting the customer would never usually know it had tripped after hot water had been turned off.

 

[DP]

namsag read what the regulars have posted.

Water in the primary side (CH side of the boiler) is heated in the main heat exchanger. This is circulated internally in the boiler to TRANSFER heat to cold water in the secondary heat exchanger when a hot tap is run. If there is little or no water in the primary loop, circulation prooving circuit will overide boiler operation.

Vaillant would appear to be one of the very few makes that can be used without an external bypass. Most makes require an external bypass depite the fact that internal is fitted. Bypass if fitted to protect the pump. Heat dissipation has to be to the heating load.

 

[namsag]

Dp read what i have written "with built in filling loop" in which case you can turn off isolating valves and just pressurise the boiler up to what ever pressure the manufacturer recomends so there would be the correct amount of water within the boiler to ensure proper heat transfer and working pressure of any incorporated flow switches.. Of hand i cannot think (not to say there isn`t) of any new main stream domestic combi manufacturers who recommend a purpose made extrenal by-passes Baxi , Potterton, Worcester,Valiant and ideal don`t (leaving trv off one rad is not a bypass). And it was after reading what regulars wrote saying that boiler couldn`t work which is cleary wrong that i replied. Not saying it is the correct thing to do but it would work, which was the arguement. And pump over run is not to protect the pump it is to help stop scale formation which occurs at temps over 60 degrees C. That is why on boilers that have tempreture controlled pump over runs it will stay on some times and not others as opposed to some boilers that use an internal timer on the board.And some manufacturers even use the fan on the appliance to pull the heat through the boiler after the burner has shut down to aid cooling.

 

[DP]

Surprise surprise fitting a Ravenheat (client supplied) combi boiler. Guess what they said about the bypass? External bypass REQUIRED.

 

[Bahco]

What a can of worms
Anybody else saying that the boiler will not heat hot water only as I will gladly prove them wrong