Draining CH but maintaining Hot Water

[dalesman]

I am about to replace several radiators so will be draining down the system for about a week.
Will I still be able to use the hot water system? If so, do I need to do anything apart from turning the CH control to off?
My boiler is a Worcester Bosch Greenstar HE combi, model ZWB 7-27 HE.
Thanks in anticipation.

 

[Agile]

Pressurise system to 1.5 Bar and then turn BOTH CH isolating valves under the boiler to OFF.

Then drain system and the boiler will remain pressurised and provide DHW.

Keep an eye on the pressure as the boiler sill stop working if it falls for any reason.

Dont forget the chemicals when you refill.

Tony

 

[dalesman]

Pressurise system to 1.5 Bar and then turn BOTH CH isolating valves under the boiler to OFF.

Then drain system and the boiler will remain pressurised and provide DHW.

Keep an eye on the pressure as the boiler sill stop working if it falls for any reason.

Dont forget the chemicals when you refill.

Tony

Tony - Thanks for your prompt reply. I take it that the boiler pressure must be maintained even when the CH system is empty?

 

[bungditin]

You need to be carefull because on some boilers the heating side is used to dump the hot water out of the boiler to cool down so isolating the valves may be an issue.

 

[bengasman]

Though this has been done before, I would not recommend it, unless you have a way to let excess heat out safely, and there is a gurantee that nobody is able to turn the ch on.
Haven't checked the M.I., but I am not quite sure it is allowed on this model in the first place.

 

[dalesman]

Thanks for your replies.
I'm a bit worried now as I have already done as Agile suggested - turned off the CH flow and return valves, although I haven't drained down the system yet.
The hot water has been used continuously since, for washing up, showers etc., and I've not heard any unusual noises from the boiler to indicate overheating.
Is there a suggested method of releasing heat from the boiler?

 

[Metasis]

The best method of release is into the central heating system, however your dear friend Agile has given you a way out considering that it is a combi boiler. Either he has taken into account the fact that there may be an internal bypass or he is hoping your boiler will blow up, either way I'm pretty sure you should be ok doing what you are doing... may God have mercy on anybody nearby. Just kidding, I'm sure a RGI can help you!

 

[Agile]

Most combi boilers end up working like than either when all the rads have been turned off or all TRVs have closed.

I have never seen a boiler damaged by operating like that.

In this case I had expected that the OP would have ensured that the heating was not switched on. Even if it was its still not likely to do any harm.

All the boiler protection, PRV and temperature controls remain effective.

I have also seen several combis used a water heaters with no problems arising.

Tony

 

[dalesman]

I emailed Worcester's Technical section to ask about this - this is their reply:

"The boiler would essentially work for direct hot water (DHW) with the flow and return isolated and with pressure still in the boiler, however there is no integral bypass within the boiler meaning the chances are high that the boiler would go into overheat. This overheat state may cause damage to the components within the boiler and as such we cannot recommend this."

So - it looks like I'll just have to have the whole system down and boil a few kettles!

Anyway, thanks for your replies and advice, at least I'm a bit wiser now!

 

[Agile]

All manufacturers are bound to give that reply as otherwise you would blame them if anything happened.

The reality is that practically all boilers will manage to operate in that way as the heating circuit often gets closed off either intentionally or by a fault.

If damage was often caused then I would have been called to repair them. I have never been called to repair any and not even those combis being used just to heat hot water.

However, now that you have received that reply you should follow it as I am not permitted to advise against following manufacturer's recommendation.

Tony

 

[oldman2]

I have followed this with interest as I wish also to shut off and drain my 28i junior ch circuits for a few weeks while having hot water still operational.
dissapointing reply from Bosch.

I take it that if an overheat were to happen in summer while the ch was turned off on the stat and to frost on the boiler control that it would send water to the only rad in the home without a trv (in my case a towel rad) assuming summer temperatures?