central heating pump over run MTVs close

E

elmsoft

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• 16 Dec 2019

• #1

My (old) Potterton boiler has an off delay for the pump. When the MTV switch lives click off a permanent live allows the pump to continue for a short while to dissipate excess heat.
But what I don't get is this;
What is the point of running the pump if both MTVs are closed, effectively isolating the boiler? Presumably they stop the water flow anyway?
The boiler has an additionalcut out and I am having to reset it from time to time. I'm guessing that if the timer switches the valves shut while the boiler is firing then the boiler overheats and the cut out operates. Next time the timer calls for heat the boiler doesn't respond and has to be manually reset. Bit of a nuisance on cold mornings.

 

Madrab

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• 16 Dec 2019

• #2

The system should have a bypass fitted.

 

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elmsoft

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• 16 Dec 2019

• #3

Thanks for reply
Is this the bypass?

 

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Terrywookfit

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• 16 Dec 2019

• #4

It would appear to be ..yes.

Dog rough and unsuitable fitting though.

 

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elmsoft

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• 16 Dec 2019

• #5

OK!!
Anyone got a link to a better way of doing it?
Thanks for your advice.

 

ianmcd

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• 16 Dec 2019

• #6

https://www.screwfix.com/p/straight...VCbLtCh3jqQHmEAQYASABEgJ4D_D_BwE&gclsrc=aw.ds

replace the existing ballofix valve and replace it with one of those

 

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elmsoft

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• 16 Dec 2019

• #7

Wonderful! I am so embarrassed not to have sorted this myself!!
Thank you so much!!!!

 

Madrab

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• 16 Dec 2019

• #8

You will need to increase the pipe size where the ISO valve is at the moment from 15mm to 22mm. Either that or you'll need a 15mm valve which aren't easy, nor cheap to get.

Worst case put a proper 15mm gate valve in there. Do remember though bypasses, whether manual or auto need to be setup properly.

 

EFLImpudence

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• 16 Dec 2019

• #9

elmsoft said:

My (old) When the MTV switch lives click off a permanent live allows the pump to continue for a short while to dissipate excess heat.

Click to expand...

It can't be a permanent live, can it?

 

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Nige F

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• 17 Dec 2019

• #10

Madrab said:

You will need to increase the pipe size where the ISO valve is at the moment from 15mm to 22mm. Either that or you'll need a 15mm valve which aren't easy, nor cheap to get.

Worst case put a proper 15mm gate valve in there. Do remember though bypasses, whether manual or auto need to be setup properly.

Click to expand...

You might get a pair of reducing sets 22/15 for rhe compression ends of the 22 valve . But it might still be too long

 

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Nige F

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• 17 Dec 2019

• #11

elmsoft said:

Wonderful! I am so embarrassed not to have sorted this myself!!
Thank you so much!!!!

Click to expand...

Don't be embarassed ! just click on thanks - it appears under "quote" on the blue bar with your cursor DiY help is the name of the game.