Power cut = likely heat exchanger damage?

[p7777m]

How does a modern low-water-content condensing boiler cope with a power cut? It's not possible for the pump to run on in order to dissapate heat - so should I expect likely need for heat exchanger replacement every time there's a power cut when the boiler is at full tilt?

 

[scatmanjohn]

so should I expect likely need for heat exchanger replacement every time there's a power cut when the boiler is at full tilt?

No. It will be fine.

 

[Agile]

Its not ideal or in accordance with maker's instructions for pump over run.

But they dont state that an UPS is required.

Once the 80 litres or so of water is circulating round a system the water does have a little momentum so that will provide a small continued circulation for a very few seconds.

In practice it rarely seems to cause any damage.

Tony

 

[p7777m]

Once the 80 litres or so of water is circulating round a system the water does have a little momentum so that will provide a small continued circulation for a very few seconds.

I guess it's just bad luck if you get a power cut at the moment the last heat-requesting zone shuts down - no circulating water to carry away residual heat.
How quickly do 2 port valves open or close (depending on type) when power is withdrawn?
Which type of valve (open when no power or closed) is normally (always?)used for zone control in domestic heating circuits?

 

[Dan Robinson]

Spring closed is the most normal... travel under normal spring is probably around 5 seconds.

I doubt that momentum has much effect in a modern boiler?

But it would be unlucky indeed if the boiler was at full tilt and suffered from that kind of thermal shock.

Mid position valves will always have a channel open for what it would b worth in this situation.

 

[Agile]

The boiler should have a pump and auto bypass valve.

Motor valves power open in about 1-2 secs and close with spring pressure in about 0.5 secs.

Tony

 

[Dan Robinson]

 

[p7777m]

The boiler should have a pump and auto bypass valve.

Yes indeed... but isn't there a bit of a debate going on about the compatibility of variable speed pumps such as the Grundfos Aplha and auto-bypass valves?

 

[Agile]

There is no debate!

Just someone who does not seem to understand that a constant pressure smart pump cannot create an increased pressure to open an auto bypass valve!

Tony

 

[adlplumbing]

no it won`t damage the heat ex
why had power cut and it`s gone?

 

[p7777m]

There is no debate!
Just someone who does not seem to understand that a constant pressure smart pump cannot create an increased pressure to open an auto bypass valve!

We're probably both thinking of the same heated debate you had a month ago on this forum about auto-bypasses
Having read that (and much elsewhere) + your statement here it's still not clear to me, given that I want to have a Grundfos Alpha, whether that creates a conflict with the boiler requiring an auto-bypass as a saftey mechanism in case all zones shut down and result in there being no circuit in which to dump heat.
Would you mind explaining please?
Going back to your comment about zone valves shutting upon power failure in 0.5 secs, I guess that would indeed be enough time for the closong circuit(s) to carry away the bulk of the damaging residual heat provided the latent heat of the boiler is relatively low (and I suppose it is for modern designs) *and* provided the gas shuts off much quicker than 0.5 secs... how long does it take?

why had power cut and it`s gone?

No. Evaluatiing installation proposal and checking whether I need to explore improvements in design or component choice to get better reliability and efficiency. See:
//www.diynot.com/forums/plumbing/new-boiler-how-ensure-efficient-operation.298711/
and
//www.diynot.com/forums/plumbing/domestic-zone-control.298710
Also, read somewhere (on here I believe) someone reckoning the heat exchanger would fry if there was no flow for some particular reason which was being discussed, and it got me thinking about other ways that sudden uncontrolled no-flow situiations may ccur.

 

[Agile]

You have not mentioned your boiler make and model.

There is no point repeating that discussion here. It was over done there.

Just accept that constant pressure pumps and auto bypasses are mutually not compatible.

Tony

 

[Dan Robinson]

Nor are they a safety device.