Adding a pump overrun

[Dave Plowman]

With a *proper* heating/hot water system, the pump will run anyway when heating the water.

[Ed Sirett]

The root problem here is nothing to do with needing an _overrun_ on the pump we need the pump to _run_ when the boiler is on, that is how older low-tech boilers work.

[Ed Sirett]

Which is the bog standard way of doing things for this type of installation.

[Bob Smith]

So why has the boiler got that problem in the first place?

Bob

[swoopdave]

replying to Ed Sirett, swoopdave wrote: What keeps the 3 way valve open to the rads while its over running?

[alan_m]

This must be a record for homeownershub - a question posted 14 years ago

[John Rumm]

I presume this is reply to a very ancient post since Ed has not posted hear for ages. However you will probably find what you need here:

[harry]

[tabbypurr]

I don't really think he needs a reply 14 years later. FWIW a fan timer is c heaper.

[Andrew Gabriel]

Why does it matter which way it's open during overrunning?

[John Rumm]

If its open to the DHW, and that is already satisfied, you won't dump much additional heat from the primary circuit into the cylinder - and will lose more out of the flue than you would expect if overruning through the rads.

[Roger Mills]

And if it dumps it to the CH, and all the rads have TRVs which are closed, it won't have anywhere at all to go.

[Fredxxx]

Wouldn't that have been happening before the boiler turned off?

[John Rumm]

The boiler would probably cycle off on its own stat in the circumstance.

Just one of those cases of not being able to win em all!

[Dave Plowman (News)]

Thought it wasn't recommended to have TRVs on every rad?

I have none in the living room and that's where the main temperature sensor is. Every other rad has a TRV.

[John Rumm]

Its isn't generally - although you do find some systems that have no main stat and have all TRVs.

(Some systems have a bypass to ensure there is always an available path for flow, and some modern boilers include an internal one (as does my Vaillant for example)).

Yup, similar arrangement here - although I have a second zone upstairs where all the rads have TRVs, you get enough heat leakage into the landing (where the zone stat is) from downstairs to satisfy that stat anyway.

[john coen]

replying to IMM, john coen wrote: have to be careful sending an unprogrammed live feed back through to other stat, Stats are tempermental

[Fredxxx]

Did they have pump overruns in 2003?

Given the OP (ARW) is an electrician you might think he knows this and a lot more besides.

This might assist you with posting to a newsgroup, albeit through a website:

- If you are sending a reply to a message or a posting be sure you summarize the original at the top of the message, or include just enough text of the original to give a context.

[Roger Mills]

Yes - long before that. My c1990 Baxi Solo (still going strong!) has one. They came in with the physically smaller boilers with aluminium heat exchangers - designed for fully pumped systems - whose residual heat could cause them to overheat if the flow stopped immediately when the flame was cut.

Having said that, the over-run logic on my boiler is somewhat flawed - and there are some circumstances which can still result in an overheat trip - so I have added a timer as well.

[Fredxxx]

I did add the comment with tongue firmly in cheek!

I recall fitting a boiler 20 years ago which in my opinion had the overrun timer set for far too long.