Boiler advice (lukewarm central heating, boiling hot water)

Vistrix

My 18 year old boiler pumps lukewarm water around the radiators in the whole house.

When we turn up the thermostat to activate the heating, the boiler fires up for about 3-5 mins and then stops. It will then continue to start for just a few seconds and then stop. It does this every every few minutes.

If I feel the central heating pipe (don't know the exact terminology!) coming directly from the boiler, its hot / close to lukewarm. As are all the radiators.

If I turn on the hot water from a tap, the smaller pipe coming from the boiler almost immediately gets boiling hot.

I know its 18 years old but this boiler recently heated every radiator in the house to the point where it would be nearly too hot to touch.

I want to check if there is anything else I can do before calling an engineer and perhaps get a very rough cost estimate on the repair so I know how much to expect!

Its a combi Ferroli Modena 102.

Thank you.

NSG666

Combi? Make Model?

Bendy_House

Vistrix said:

My 18 year old boiler pumps lukewarm water around the radiators in the whole house.

When we turn up the thermostat to activate the heating, the boiler fires up for about 3-5 mins and then stops. It will then continue to start for just a few seconds and then stop. It does this every every few minutes.

If I feel the main water pipe (don't know the exact terminology!) coming directly from the boiler, its lukewarm. As are all the radiators.

If I turn on the hot water from a tap, the same pipe almost immediately gets boiling hot.

I know its 18 years old but this boiler recently heated every radiator in the house to the point where it would be nearly too hot to touch.

I want to check if there is anything else I can do before calling an engineer and perhaps get a very rough cost estimate on the repair so I know how much to expect!

Thank you.

As NSG asks, make and model and type of boiler, please.

At the moment, what you describe doesn't make sense - the same pipe coming out of the boiler shouldn't be supplying both the rads and the 'instant' DHW.

A photo would also help, showing the pipes involved.

If you are saying that there's a pipe that becomes hot almost immediately when a hot tap is opened, then I'm guessing that pipe is 15mm size, and doesn't also supply the rads.

Unless you have a weird boiler with a built-in DHW storage.

Vistrix

Bendy_House said:

Vistrix said:

My 18 year old boiler pumps lukewarm water around the radiators in the whole house.

When we turn up the thermostat to activate the heating, the boiler fires up for about 3-5 mins and then stops. It will then continue to start for just a few seconds and then stop. It does this every every few minutes.

If I feel the main water pipe (don't know the exact terminology!) coming directly from the boiler, its lukewarm. As are all the radiators.

If I turn on the hot water from a tap, the same pipe almost immediately gets boiling hot.

I know its 18 years old but this boiler recently heated every radiator in the house to the point where it would be nearly too hot to touch.

I want to check if there is anything else I can do before calling an engineer and perhaps get a very rough cost estimate on the repair so I know how much to expect!

Thank you.

As NSG asks, make and model and type of boiler, please.

At the moment, what you describe doesn't make sense - the same pipe coming out of the boiler shouldn't be supplying both the rads and the 'instant' DHW.

A photo would also help, showing the pipes involved.

If you are saying that there's a pipe that becomes hot almost immediately when a hot tap is opened, then I'm guessing that pipe is 15mm size, and doesn't also supply the rads.

Unless you have a weird boiler with a built-in DHW storage.

Bah, you're right, sorry. Its the left most pipe for the central heating, a larger one. It can get fairly hot but not as hot as the smaller hot water pipe.

The boiler is a combi Ferroli Moderna 102.

I'll update the original post...

Bendy_House

Sorry...can't...type.... Your boiler is called...weeps...'Moderna'.

Cough - soz.

Ok, I've narrowed it down to one of two things - the external controls (eg the room thermostat) or the boiler...

(You're cold, yes? You ain't finding this funny, no? :-(  )

When you turn the 'stat up for heating, does the relevant green light come on on the boiler to indicate a call for heat?

This is an old boiler, and looking at an exploded diagram (hopefully not predicting the near future) this boiler does not appear to have a 'diverter valve', the part I was going to mostly suspect.

Instead, it would appear (but I'm not sure) that both heat exchangers - the one for the CH and the one for DHW - are part of the same assembly. So, when you turn on a hot tap, the water flow is detected and the boiler is told to burst into life. And when you turn up the room 'stat, the boiler is told to fire up AND the CH pump (inside the boiler) also comes on to circulate the water around your rads.

Clearly your actual boiler is firing up ok, but it seems to struggle to pump water around the rads, and instead the boiler shuts down after a few minutes of trying. This is a normal safety effect - if the pump isn't running, the hot water gets far too hot in the exchanger and would start to boil. Therefore a safety stat inside simply shuts the boiler down.

I suspect it's something like the pump not working, but that's just my best guess.

If the room stat appears to be controlling the boiler correctly - ie you turn it up and the green light comes on and the boiler fires up - then the external controls would seem to be working just fine. The remaining symptoms point to a boiler that's 'working' - ie firing up ok - but cannot shift the CH water. Most likely candidate is the pump. Ie, you need a GasSafe :-)

Vistrix

Bendy_House said:

Sorry...can't...type.... Your boiler is called...weeps...'Moderna'.

Cough - soz.

Ok, I've narrowed it down to one of two things - the external controls (eg the room thermostat) or the boiler...

(You're cold, yes? You ain't finding this funny, no? :-(  )

When you turn the 'stat up for heating, does the relevant green light come on on the boiler to indicate a call for heat?

This is an old boiler, and looking at an exploded diagram (hopefully not predicting the near future) this boiler does not appear to have a 'diverter valve', the part I was going to mostly suspect.

Instead, it would appear (but I'm not sure) that both heat exchangers - the one for the CH and the one for DHW - are part of the same assembly. So, when you turn on a hot tap, the water flow is detected and the boiler is told to burst into life. And when you turn up the room 'stat, the boiler is told to fire up AND the CH pump (inside the boiler) also comes on to circulate the water around your rads.

Clearly your actual boiler is firing up ok, but it seems to struggle to pump water around the rads, and instead the boiler shuts down after a few minutes of trying. This is a normal safety effect - if the pump isn't running, the hot water gets far too hot in the exchanger and would start to boil. Therefore a safety stat inside simply shuts the boiler down.

I suspect it's something like the pump not working, but that's just my best guess.

If the room stat appears to be controlling the boiler correctly - ie you turn it up and the green light comes on and the boiler fires up - then the external controls would seem to be working just fine. The remaining symptoms point to a boiler that's 'working' - ie firing up ok - but cannot shift the CH water. Most likely candidate is the pump. Ie, you need a GasSafe :-)

Ha! Modena*. I had to double check that...

Thanks for your reply. The light does come on when I turn up the thermostat for heating so I didnt think it was the controls.

I was thinking maybe the central heating needed a flush or do you not think this could be the issue?

Replacing the pump sounds expensive...is it?

Bendy_House

I suspect not for that model - it'll be a basic single-speed jobbie, most likely.

However, a quick search also suggests it could be one of these fancy 'obsolete' models. (You still ain't laughing...)

Ferroli Part No: 39804810 (But don't quote me) Try a google and see if you can find one. Bound to be one somewhere.

However, we don't actually know if it is the pump - that's only a guess.

Sludge? Yes, a possibility, but unlikely to have reduced a hot system to now't overnight.

Bendy_House

Your boiler is old and non-condensing. Expect some pressure to have it replaced. However, if it IS the pump and IF one can be found, no reason you shouldn't keep it trucking.

Bendy_House

I can't find that part number, but a search for Ferroli 102 pump comes up with part number 39808310, and pump 'heads' (ie the main part) come up for these quite commonly, and for reasonable sums - around £60.

Eg: https://www.ebay.co.uk/itm/124337760337?chn=ps&mkevt=1&mkcid=28

https://www.ebay.co.uk/itm/363493174361?

But I don't know if this is the right part.

Vistrix

Thats great, thats helped me out lots.

Thanks for all of your advice!

Bendy_House

Let us know how it pans out.

Do you know of a good, local GasSafe you can call?