Pump overrun “working” but not giving up heat

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Why not make it simple?

Add a relay to open a motorised valve, so the heat is piped into another part of your system?

lol - my wife said that to me earlier today. I think she’s either a genius or has a part time job as a plumber :)

Thing is, as you may know, the motorised valve when open calls the boiler to come on. So it’s not that straightforward. Not impossible but not “simple”

NOTE: one post I read elsewhere said to plumb in a bypass AFTER the motorised valve. I’ve seen lots of other ideas but dismissed them for various reasons.
 
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Thing is, as you may know, the motorised valve when open calls the boiler to come on. So it’s not that straightforward. Not impossible but not “simple”

You said you had a fancy relay system, it cannot be that difficult to interrupt the feed from valve to boiler, to inhibit the boiler seeing a demand when the valve is opened.
 
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You said you had a fancy relay system, it cannot be that difficult to interrupt the feed from valve to boiler, to inhibit the boiler seeing a demand when the valve is opened.

I could do it yes, YOU said it was a simpler solution :p :D

Attaching some extruded alu to the copper is looking like plan A......
 
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she is probably a member of the secret womens website where they discuss such things. It is disguised as a baby care website to keep plumbers away.

It is also where they discuss the DIY capabilities of their menfolk.
 
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maybe you’re right, but I always thought the idea was to bring down the temp slowly of the exchanger and then switch off when temp is lowered

my post was also to elicit replies like yours, questioning the premise of what I’m trying to do. Because yeah, maybe I don’t quite get the point of overrun

What happens to the water temperature whilst the pump overrun is running? Why do you believe what is happening is insufficient?

My boiler (Vaillant 438) had approximately 3m of pipe between flow/return through an ABV (had, as I now have a LLH, but the pipe run is still relatively short). The idea was to keep the water circulating and allowing it to slowly cool down. Even on such a short run, the temperature drop would be quite dramatic initially.

Stress on the hex is caused by the delta T of flow and return being too high. In the pump overrun scenario, the flow and return temps are roughly the same.

Maybe I've got it all wrong - but sounds like you're trying to solve a problem which doesnt exist.
 
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What happens to the water temperature whilst the pump overrun is running? Why do you believe what is happening is insufficient?

My boiler (Vaillant 438) had approximately 3m of pipe between flow/return through an ABV (had, as I now have a LLH, but the pipe run is still relatively short). The idea was to keep the water circulating and allowing it to slowly cool down. Even on such a short run, the temperature drop would be quite dramatic initially.

Stress on the hex is caused by the delta T of flow and return being too high. In the pump overrun scenario, the flow and return temps are roughly the same.

Maybe I've got it all wrong - but sounds like you're trying to solve a problem which doesnt exist.

my boiler is set to high (need to turn it down now we have warmer weather) so sits steady at say 87 when heating the hwc etc (usually I set it to around 70-77 degrees or lower, anyway...)

and when the overrun comes on it can increase to say 90 or 91 in the first minute or two and then it comes down slowly to say 81 and then say 76 after 3-5 minutes

initially I thought the pump wasn’t actually moving any water but I can feel (touching the pipes) that it is, and I can hear the pump working properly too and not just spinning not moving water

yeah it might not be a big issues because it does “work” but my old setup, which had a much higher capability to lose heat in the f/r runs, I used to remember the heat almost instantly came down and continued to come down

it’s not the biggest issue I have to work on at the minute but it doesn’t feel it’s working as I’d hoped.
 
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I'll admit I've not read the entire thread, so possible I'm just asking what you've already looked at: What are you doing with all your diverter valves? While they are all open with overrun, then you're having colder fluid pushed into the return of the boiler. As soon as you start shutting them off, the temperature of the return is going to go up as you're valving out the various heatsinks. With no heatsinks, the return will pick up water from the flow, PLUS the residual heat in the exchanger - explaining why you see the temperature increase briefly then come down again.

Nozzle
 
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and when the overrun comes on it can increase to say 90 or 91 in the first minute or two and then it comes down slowly to say 81 and then say 76 after 3-5 minutes

That is to be expected, if the water has no where to go/ the same water is staying in the heat exchanger. You need to find an easy way to ensure a valve can remain open, for the overrun period.
 
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Yeah the more I’ve thought about this today the more obvious is was always doubtful the heat would be able to be shed. It’s never been my number one issue to be honest, more an annoyance

it was sort of done as an afterthought, along with a thousand other things at the time when building my house.

Also, the previous system was crap. HWC was in loft!! And boiler in garage. With a long run in 22mm plastic crap. That overrun REALLY shed the excess heat, because the whole system was inefficient. All ripped out and gone now.

so giving up heat in the new much MUCH more efficient design actually, perversely, becomes more difficult.

Two things I’ll try:

  1. Extend relay timer so overrun runs for longer. Won’t reduce rate of heat loss but will leave temp lower ultimately
  2. I have a small unused rad I could hook in as a “heat sink” (this won’t be done for a while, but would work better)

thanks for all the constructive comments/help
 
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Two things I’ll try:

  1. Extend relay timer so overrun runs for longer. Won’t reduce rate of heat loss but will leave temp lower ultimately
  2. I have a small unused rad I could hook in as a “heat sink” (this won’t be done for a while, but would work better)

You are overthinking the need for it. All you need to aim for, is removal of the residual heat in the heat exchanger - to get it's temperature down to that of the rest of the system and prevent the sudden removal of the cooling flow of water, allowing the temperature in the heat exchanger rising. You can do that by running the pump for a few minutes with a valve open, to distribute the heat.
 
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You are overthinking the need for it. All you need to aim for, is removal of the residual heat in the heat exchanger - to get it's temperature down to that of the rest of the system and prevent the sudden removal of the cooling flow of water, allowing the temperature in the heat exchanger rising. You can do that by running the pump for a few minutes with a valve open, to distribute the heat.

no, I’m not overthinking it. I’m thinking what can I do now, quickly, because I have a load of other things to do. And what is the medium/longterm solution. I could, for example, do nothing.

1. Above is the quick 2 second fix. I’ll do that.

In the longer term I’ll think what to do. I could certainly run it through the (yet to be added) single rad circuit with two rads on it.

Knowing what solution to do is the first challenge
 
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Can't you just wire the pump and heating valve in parallel?
 
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Can't you just wire the pump and heating valve in parallel?

no. It’s not that simple.

it’s a “S-Plan plus plus”. It’s a verge large house with a complicated design using 3 pumps (lots of ufh) and 4 ZVs

if you know anything about ZVs you know they close a mechanic switch that calls the boiler when they open. So this defeats the idea you suggest.

You can do anything electronically, but even I have my limits

for those interested this is the “falling edge” relay I used. Brilliant bit of kit solves all kinds of problems.

Cycle Timer-GRT8-B1 Mini Power Off Delay Time Repeat Cycle Timer Relay DIN Rail Type AC 220V https://www.amazon.co.uk/dp/B07V7FC...abc_KV0SNRN0WZ29DDT9Z0H6?_encoding=UTF8&psc=1
 
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