7 head pump upgrade on an Intergas boiler

[evets51]

I've got quite a longstanding problem with a 1.5 year old 18kw Intergas system boiler which takes over an hour to get all radiators hot - and even then they aren't scalding hot to the touch even though the water temp is set to 80 on the boiler.

Potted history - it was a replacement boiler we had put in when we moved in, to replace a 17kw Ideal boiler. Its a 5 bedroom / 17 radiator house, approx 2200 sq ft - most people seem to think the boiler is too small, however having put my details into the boiler size calculator at idhee.org (double-glazed, 270mm loft insulation, cavity wall insulation) it came up with 13.6kw. Also the previous owners, who I trust, assured me the previous lower capacity Ideal boiler coped adequately.

Its a microbore system - originally sludged up badly and heating performance was awful (rooms wouldn't heat up at all), but we had 2 power flushes done plus a load of Fernox sludge remover. The three worst radiators for getting hot are in the living room and hallway - I've taken these radiators off and run a hose through them and no sludge, so I'm reasonably sure the system is clean.

The boiler shortcycles all the time - so fires for the first 2 or 3 minutes, then backs off for another 2 minutes or so before firing again etc. If it was firing constantly and took an hour or more to heat up I'd believe it was undersized - but it can't be right for it to be shortcycling constantly like this? So yesterday I closed off all radiators other than the three which are the worst performers, and fired up the heating. All 3 radiators got red hot within 20 minutes (hotter than I've ever felt them) - hot at the top and bottom (even though the boiler still shortcycled).

Its been suggested that the problem is the pump not being able to move the water around the system adequately. I've no idea what the pump system on the Ideal was. I've spoken to Intergas and they tell me the pump on the current boiler is a "5 head" pump, but you can get a "7 head" pump as an upgrade - £140 for the part. Just looking for opinions on whether or not that is likely to be a big help and worth trying? We've spent quite a lot of money on powerflushes / having people in to add Fernox and drain the system etc, and one of the options on the table at the moment is ripping the whole system out and adding all new radiators plumbed in 15mm copper with a new, bigger boiler. Obviously that's going to cost a small fortune though so would like to avoid if possible!

 

[happyflyer]

You need someone to come and look at the whole system, where do you live?

Boiler does appear on the low side, I would work out the heat losses for each room properly

 

[johnnyplumb]

was the heating working ok after the new boiler was installed

 

[evets51]

You need someone to come and look at the whole system, where do you live?

Boiler does appear on the low side, I would work out the heat losses for each room properly

I'm near Cambridge, we've had several people come to look at the whole system and provide estimates etc but opinion has been divided so far between getting another powerflush done, getting a new bigger boiler, getting the whole system repiped etc. So just trying to canvas as wide an opinion base as possible really.

No the heating never worked when the new boiler was put in - the powerflush that was done as part of the boiler install was done off one of the radiators. This is why we later had a second flush done from the flow / return pipe on the boiler - which was much more effective. That (and the Fernox stuff we'd had put in in the meantime) really improved the performance a lot as originally it took 3 / 4 hours to get the house up to temp. These days if its 1/2 degrees outside it takes approx 1.5 / 2 hours to get 19.5 inside - much better but still could do with improvement.

 

[happyflyer]

You will get all sorts of people guessing, there may be a number of problems not just one, that's why they guess, you need one man who knows what he is doing
and your problems are over, trying to fixed with such deep routed problems will be difficult, if you don't get someone to physically come and look at it you will go round
in circles, sorry I am not nearer maybe there is a member near you, these people don't usually fail because they come back and tells us all how they fixed it.

See if some does pop their head above the parapet for you.

Good Luck

 

[galaxy_plumbing]

sound like poor circulation. does furthest radiator get hot? as said, its hard to help over internet in this case.

 

[Killy Bing]

Get an engineer off this forum, that pump should be more than capable.

I suspect that the issue would be more due to system layout.

the previous owners said the old boiler was capable but as you also said the system was sludged up badly.

Has there been any extensions in the past?
has the boiler been moved?
what had the ideal boiler replaced or was the the original?

 

[evets51]

Get an engineer off this forum, that pump should be more than capable.

I suspect that the issue would be more due to system layout.

the previous owners said the old boiler was capable but as you also said the system was sludged up badly.

Has there been any extensions in the past?
has the boiler been moved?
what had the ideal boiler replaced or was the the original?

Yes 2 extensions in past - a big bedroom / en-suite / wardrobe over the double garage (1 large, 1 small radiator in there plus heated towel rail which is the bypass circuit) and conservatory (2 radiators plumbed in series so only 1 ever gets hot! - doesn't matter as we don't use conservatory in winter). Extensions were 5 years old for bedroom and 10 for conservatory when we moved in - so they'd lived with them for a while.

Ideal was the original house boiler - been there since 1993 when it was built. There is another house of exact same build in our street (including extensions) which had the same boiler and same microbore etc and they said it worked fine for them too.

Boiler is in the same place as it always was. The big bedroom is the longest throw from the boiler - approx 8.5 metres from the airing cupboard to the radiator. Its the worst performing of the lot but I don't really care as don't like a warm bedroom. Funnily the small radiator in the wardrobe (same distance) performs well.

The lounge and hallway are the ones I really care about - they haven't been altered since the house was built.

 

[oz-plumber]

Hi evets,

What the problem could be is that the radiator valves are not opening enough.
If you have the original radiator valves, particularly the thermostatic types, the valve can get stuck in the closed, or near closed position.
Before you go ahead and replace the boiler or pump, remove the thermostatic heads and pull the metal pin up with a pair of pliers.
I would say - from the information you have provided - that this could be the issue.
Or the lockshield valves are not opened up enough - valve on returns side of heater.
If the boiler was too small there would be no way it should be short cycling, it would be going flat out all the time.

Oz-Plumber

 

[Gas]

You size boilers for the hot water demand, not heating. I would get this system balanced properly using the two thermometer method, getting the correct temps on the flow and return and sorting out the bypass in the process.

I would put money on this sorting it.