Boiler stat or pump over run stat...? You decide...

[JimboGog1]

Hi again,

I posted a topic a few days ago regarding my Ferroli boiler as per below:

“I have a gravity fed gas boiler with four 1 inch feed pipes. Two which feed the radiators and two which feed the hot water system. Although old, the boiler has worked fine up until now...

Now however, every time the pump winds down it sends a surge of boiling water from what appears to be the boiler all the way through the hot water pipe, through the hot water cylinder (located in bathroom) and then up to the expansion tank in the attic. When this happens, the pipes make an almighty racket and physically contract under the pressure/ heat. This last for a few seconds every time the pump switches itself off

One second you can have your hand on the hot water feed pipe and the next second it is literally too hot to touch and then cools down almost as instantly – making some very laud scraping, moaning, banging noises.

I have been up to the attic and the expansion tank, although not overflowing is very hot.”

It was suggested that the problem relates to either my boiler stat or my pump over run stat so I guess my next question is:

1) Where is the pump over run stat and where is the boiler stat?

2) How can I be sure it is one of these i.e. how will I know if they are broken, is there a test I can do?

3) Do I need to call a boiler repair man to replace either or, or could my farther in law who is an industrial pipe fitter fix it i.e. not much work needed to the internals?

Cheers

 

[Ronald0]

Seems that your pump has lost its ability to continue running for some minutes after the boiler has shut down,

This pump over-run is generally controlled by a pump delay thermostat which is located on the side of the heat exchanger within the boiler case. (I am not familiar with the Ferroli boiler; do the have the manual to confirm?)

This can be replaced or a test link wire can be put across to force it closed.

The boiler overheat stat (if it has one) as opposed to the boiler control stat is a thermal overload safety cutout to switch off the boiler in an overheat situation.

 

[JimboGog1]

Brilliant thanks Ronaldo.

So you think it’s the over-run too?

Can you please confirm (and sorry for my ignorance) what a test link wire is, what will it do and how do I do it?

Also, will this be a permanent fix or just a way of seeing if it's broken?

Thanks ever so much for your help with this.

 

[Ronald0]

Jimbo, you need to confirm that your boiler requires pump over run; do you have the manual?

If it does, confirm that the pump does not continue to run after the boiler shuts down.

You then need to make the pump run independantly to see if it prevents water from boiling and expanding up the vent pipe.

How you do that depends upon your level of expertise.

Are you able to disconnect the pump and power it from a 13A plug to test it?

A test link will bypass the pump delay thermostat and connect the permanent live to the boiler, to the pump so that it runs whenever the isolator is on.

Do not work with mains electricty unless you are competent to do so.