Radiators not piping hot last year

Several years ago (maybe 5) in winter; I left the central heating on when i went out for a few hours and it was unbearable when i returned. I had to leave the windows open all night due to the heat.

Last year in winter; I noticed my radiators were not piping hot when the central heating was on. Therefore I maxed out the thermostat and left it all day. Still the radiators were only warm.

I called a boiler engineer who has advised replacing the boiler. I currently have a Potterton Powermax 85HE CP. I believe it was installed when my house was built in 2002 (I moved in; in 2013) though Potterton seem to think it is more like 2007 due to the serial number. The boiler engineer has quoted circa £4K to replace my current boiler with a Worcester 4000 30KW.

I own a 3 bed (2 floors) semi detached house with a main bathroom; an ensuite and a WC. It also has a kitchen, lounge and dining room. I have two questions:

1) Is £3,179 reasonable (I have never had a boiler replaced before)? I have no idea whether this is a good price or not. I live in Lincolnshire.
2) Is the 4000 sufficient for my house or should I be looking at the Worcester 8000 35kw boiler, which was also quoted (at £3,679)

I live alone, however I am conscious that I may sell the house one day and a family may move in who have more requirements than I do e.g. multiple people requiring hot water.

They have also said they will perform a system cleanse using an inhibitor. Another company suggested a power flush for the radiators.

It might be worth trying to balance your radiators to see if you can improve performance with the existing boiler.

1) Boilers are about that expensive. To see if a price is reasonable, then get a few more quotes. You can find approved boiler installers on the manufacturer's website.

I would just get a boiler that suits your needs and not worry about anything else.

Ian1981 said:

I called a boiler engineer who has advised replacing the boiler.

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You 'called', but did (s)he attend, and investigate the problem, or just offer an opinion over the phone?

The causes of radiators can be many, though not necessarily due to a boiler fault. It needs properly investigating first, otherwise you may end up replacing the boiler, only to have the problem still there.

Sounds like another story of an installer that doesn't want to problem solve an older system, rather just wants to install a new boiler for copious amounts of cash.

I think you need someone that will look over your system and tell you why your rads aren't warming up properly, you may not even need a new boiler but if you do you want to know why.
A lot of the key components for that box but I think it needs further investigation into why the rads aren't getting up to temp. Is the HW delivery still ok/not affected?

Two engineers have turned up and recommended a new boiler. Only spent 5-10 minutes looking at the radiators. Not sure how long this should taker? (and additional cost if necessary of course).

Ian1981 said:

I called a boiler engineer who has advised replacing the boiler.

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As Madrab said: you need to find out the cause of the problems in the system first

if the system is fairly old it could be a problem with the system, such as sludge in pipes or pump rather than boiler

is the pipework 15mm or microbore?


if you do choose to replace consider alternatives to the Worcester, maybe ask for a price from somebody who does Baxi, Main or Ideal -common and popular boilers. Also ask about weather compensation.

nb boiler choice is less important than quality of installation

Ian1981 said:

Two engineers have turned up and recommended a new boiler. Only spent 5-10 minutes looking at the radiators. Not sure how long this should taker? (and additional cost if necessary of course).

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who normally services your boiler -they should have a good idea of your system.

Notch7 said:

nb boiler choice is less important than quality of installation

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Absolutely this.

Ian1981 said:

Two engineers have turned up and recommended a new boiler. Only spent 5-10 minutes looking at the radiators. Not sure how long this should taker? (and additional cost if necessary of course).

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Basically, just a sales call then, no attempt to diagnose where the problem might be.

The Powermax is an unusual design and 9 out of 10 installers won't understand it. It's basically a conventional heat only boiler combined with a small unvented cylinder. This gives an (initial) exceptional hot water flowrate to feed the extra demand when all hot outlets are in operation.
The majority of standard combi boilers can never compete on flowrate so check the specs very carefully if downgrading to a combi.
On the Powermax there were many flue types resulting in the boilers often being placed away from external walls...this can make replacement awkward.

Regarding the low radiator temp a very likely and common problem is a sticking diverter cartridge...this design in particular.
Rather than the heated water flowing to the radiators some is fed via the cylinder coil. It's an easy check to make. The bypass valve could also be partially jammed open or the pump is weak.

Notch7 said:

As Madrab said: you need to find out the cause of the problems in the system first

if the system is fairly old it could be a problem with the system, such as sludge in pipes or pump rather than boiler

is the pipework 15mm or microbore?


if you do choose to replace consider alternatives to the Worcester, maybe ask for a price from somebody who does Baxi, Main or Ideal -common and popular boilers. Also ask about weather compensation.

nb boiler choice is less important than quality of installation

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I had a plan with Baxi for many years. It originally costed £17 PCM but increased to £85 PCM over the years because of the age of the boiler. I cancelled it earlier this year because Baxi said they could not help with the radiators as it was down to sludge.

The two engineers who visited both said a new boiler should resolve the sludge issue:

1) The first said a power flush should resolve it (included with their quote).
2) The second said a system cleanse using an inhibitor should resolve it (included with their quote).

The first said a power flush is superior to a system cleanse, however my research is telling me that this is not necessarily the case?

I think the pipework is 15mm. I researched this and someone on here said if the pipes going in and out of the radiator are bigger than your little finger than they are likely to be 15mm (10mm microbore is more like the size of a pencil apparently). Someone else said a house built in 2002 is likely to be 15mm.

Gasguru said:

The Powermax is an unusual design and 9 out of 10 installers won't understand it. It's basically a conventional heat only boiler combined with a small unvented cylinder. This gives an (initial) exceptional hot water flowrate to feed the extra demand when all hot outlets are in operation.
The majority of standard combi boilers can never compete on flowrate so check the specs very carefully if downgrading to a combi.
On the Powermax there were many flue types resulting in the boilers often being placed away from external walls...this can make replacement awkward.

Regarding the low radiator temp a very likely and common problem is a sticking diverter cartridge...this design in particular.
Rather than the heated water flowing to the radiators some is fed via the cylinder coil. It's an easy check to make. The bypass valve could also be partially jammed open or the pump is weak.

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This is the impression I get i.e. plumbers can't really help because of the boiler type. Baxi themselves advised me to replace the boiler telling me 1) it is not energy efficient meaning i will save with a new boiler 2) It is not a combi boiler meaning i have to pay to heat water unnecessarily 3) I will save as i will have a 10-12 year warrenty meaning i don't have to pay insurance.

Ian1981 said:

The two engineers who visited both said a new boiler should resolve the sludge issue:

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You are being given some really bad, and potentially expensive advice. A new boiler will obviously not fix the problem. Your priority is to clean out the sludge in your system, your present boiler will then likely function just fine, if properly cleaned out.

Potentially, you could make a fair job of this yourself, by draining the system, and simply flushing it through with lots of water, depending on how bad it is.

Ian1981 said:

1) The first said a power flush should resolve it (included with their quote).
2) The second said a system cleanse using an inhibitor should resolve it (included with their quote).

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They are both trying to sell you a flush, to get the system working, then an unnecessary boiler, for extra profit. A cleanse with inhibitor, will not make any difference. That is not the purpose of inhibitor (see below). You can instead, flush as much of the dirt and debris out yourself, then run the system with some special cleanser, for a day or two, then flush it again, refill and add the essential inhibitor.

Ian1981 said:

I think the pipework is 15mm. I researched this and someone on here said if the pipes going in and out of the radiator are bigger than your little finger than they are likely to be 15mm (10mm microbore is more like the size of a pencil apparently). Someone else said a house built in 2002 is likely to be 15mm.

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It will likely be 15mm!

What has caused your problems is lack of inhibitor in your system. You have had the boiler maintained, but whoever serviced your boiler, only serviced the boiler alone - nobody looked after your heating system, nobody ensured the system had inhibitor added to it. The purpose of the inhibitor, is to prevent your full of water radiators, from rusting. The rust, turns to a sludge, which restricts the flow, and eventually blocks your radiators and pipework. Adding it, and making sure the amount in your system, is absolutely essential maintenance, but often overlooked by owners, who assume it is part of a boiler service.

Adding inhibitor, is even more essential, where a modern boiler is installed, because they have such narrow internal passages.

Ian1981 said:

1) it is not energy efficient meaning i will save with a new boiler

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True, a modern boiler can save on gas consumed, but old boilers lasted for decades and were very cheap to repair. Modern ones, last maybe 10/12 years, and are much more expensive to repair.

Ian1981 said:

2) It is not a combi boiler meaning i have to pay to heat water unnecessarily

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That, really, depends on how you use your hot water, and will likely be untrue. I would not panic to move to a combi, without giving it lots of thought. The system you have, was expensive to install, and will cost to convert over to a much more complex combi- boiler. Many people do, regret allowing themselves to be persuaded to swap the system to a combi.

Your cheapest option, is a straight replacement of the boiler you have, to the same type of boiler, but a more modern, condensing one.

Ian1981 said:

3) I will save as i will have a 10-12 year warrenty meaning i don't have to pay insurance.

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Potentially true, but only if you make sure the entire system is maintained properly, with a full service each year, and is given a thorough flush, and a special filter added.

I sent this to the plumber:

"
The reason I’m having the boiler replaced is that a few of my radiators are not working, and most of them do not get fully hot. In addition, the boiler itself is quite old.
I’ve done some research and understand that a standard system cleanse with inhibitor (which I was informed is included) may not be sufficient in my case — do you agree? It seems that a powerflush might be required to properly remove any sludge build-up.
Could you advise whether it would be best to arrange a powerflush before the new boiler is installed, or if this can be done as part of the installation process? Also, if it is possible to do it beforehand, would you be able to carry this out as a separate job prior to the boiler replacement?"

and received this back:

"
If your radiators are cold, it is a sign that there is sludge build up in the system, if you were to go ahead with a power flush you would be advised to do it before installing a new boiler, otherwise the sludge could circulate into the new boiler and cause damage.

If the system is quite old, a chemical flush may advisable instead as a power flush can cause leaks in old rads/pipework. The chemicals would be introduced and we would leave it for a few days before draining and flushing.
"

Not sure what to do.

Ian1981 said:

Not sure what to do.

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Cheapest options first, then see how things turn out. A full drain, and flush, plus a chemical flush, should get your heating system back in working order, assuming your boiler is OK, just not efficient. You can do that work yourself, for not much money.

The advise that it needs to be flushed before a new boiler is correct, and absolutely essential.

Then you can decide whether it is worth investing in a new, more efficient boiler, plus a filter. To that, you might want to include a new, more efficient control system for your heating.

Whatever, make sure that inhibitor is added to the system, before it is left, or you will soon be back in the same position as now.