What boiler?

Brie

We need to replace our boiler.  We've been saying that for 3 years at least since discussing it's lack of performance with the boiler guy when he came to service it.  Cynical me at the time thought that he was just trying to make a sale but I'm beginning to think he's got a point.

I think the boiler is about 15 years old.  Not ancient but well used.  It's a combi.

There's been 2 obvious problems.  During the real cold snap recently it just wasn't doing much to heat the house.  It may be that the overall gas pressure in the neighbourhood was strained too much or it might be the boiler.  Most days during that period the radiators would be warm to almost hot.  We struggled to get the temperature in the house above 13c.  The other problem is it won't hold sufficient pressure to switch on when required.  So turn on the hot water in the kitchen - nothing.  6am when the heating is supposed to come on - nothing.  So we have to repressurise - which obviously we can do but it's becoming more frequent.  At one point it might be every other month at most, now it can be twice a day.  

So what type of boiler should I investigate so I know what to ask for when getting something installed.  Happy just for people to give me questions to ask an installer rather than a specific brand.

[Deleted User]

Your problem is greater than just needing a new boiler. Are all your radiators getting hot: if so, they may be undersized for your home. New condensing boilers are at their most efficient when run at low temperatures. It follows that you need someone to carry out a full heat loss survey to determine whether you need to replace some radiators

 I cannot endorse these people personally but I have had dealings with a couple of their expert panel:

https://www.theheatinghub.co.uk/

BUFF

what exact make/model boiler do you currently have?
Your pressure issue sounds like it is expansion vessel related - it may just require repressurised via the schrader valve (not the filling loop) or the membrane may have gone & the vessel requires replacement.

If you do replace the boiler, what are your needs, budget & timeframe (is this your forever home or do you think that you will be moving on at some point)?

Brie

Thanks @[Deleted User]
I would expect any survey to point out the obvious that the velux windows in our sloping roof are a massive energy drain.  I'd been thinking about getting good blinds on them to keep out the summer sun but am wondering now about whether insulating ones are a possibility.  

The radiators all get hot, or all of them don't - like when it was so cold.  And currently the house is an overheated 20c.  So I don't think it's the size of the rads that's an issue.  There is just one room that is quite chilly but there's just a small rad in there and a loft room above it with no insulation so I expect it's the combination to blame for the chill.

Brie

BUFF said:

what exact make/model boiler do you currently have?
Your pressure issue sounds like it is expansion vessel related - it may just require repressurised via the schrader valve (not the filling loop) or the membrane may have gone & the vessel requires replacement.

If you do replace, what are your needs, budget & timeframe (is this your forever home or do you think that you will be moving on at some point)?

ummmm.....the boiler is about 3 feet high and 2 feet wide & deep and white (not that I'm racist)  (sorry - will need to check)

We have the money to do things in the coming year or 3 and are hoping to only leave here horizontally (if you know what I mean).

As for needs - to keep warm and not have a damp house (the downstairs bathroom is a bit of a thing, not help by a useless exhaust fan).  If there was a blown air system here (which there isn't and very likely isn't possible) I'd look at getting air con installed as well.  

NannaH

A decent boiler,  like a Vaillant ecotec pro 28, with flue kit and smart controls + magnetic filter will set you back around £1500, another £60 - £100 will get you trvs,  a decent engineer will do a system flush before installation.
You can reckon £750 - £1000 for intallation,  depending on complexity and if new runs of pipework are needed.  
 The ‘big’ firms like boxt etc.  have big mark ups and pay their sub contracting installers peanuts,  a good local, (non vat registered ) engineer will almost always be cheaper, especially if you order and pay for the boiler.
Be aware if you go through ‘check a trade’ , ‘my builder’ etc.
Every installer you connect with gets charged a fee,  probably £100+ whether you use them or not,  so if you shortlist 3 or 4 then you can see how much money these intermediaries are making! 

   If you see someone on there that you like the look of then google them and contact them direct 😉

macman

None of the detail you have given us so far (which isn't a lot) indicates any need for a replacement of the boiler. Poor performance in the recent cold weather is not the result of  'low gas pressure'. If the rads are hot, then the issue is undersizing, or poor insulation.
If it's only 15 years old, then it's a condensing model, so relatively efficient. If older than 2005, it's possibly not, which is why you've been asked for the make and model.
Failure to maintain pressure is either a faulty EV (as explained above), a sticking PRV (easily checked by putting a bag over the external drain outlet to see if it's discharging), or a leak on the CH circuit. Only the latter takes more than 5 mins to diagnose, as it may not be visible. One of the first two are far more likely, and both are relatively simple components to replace. 
If you've not had it serviced in 3 years, then now is the time.
If you do decide to replace it, the first question is: do you want another combi, or a conventional or system boiler? 

FreeBear

macman said: None of the detail you have given us so far (which isn't a lot) indicates any need for a replacement of the boiler. Poor performance in the recent cold weather is not the result of  'low gas pressure'. If the rads are hot, then the issue is undersizing, or poor insulation.

Would agree - I have a vintage Baxi back boiler (over 30 years old), and it is now comfortably heating the house to 18+°C even during the recent sub-zero cold snap. Improving the insulation levels, killing cold draughts, and balancing the radiators have all payed dividends.

If you have been unable to heat the house above 13°C, replacing just the boiler is not going to improve matters.

Olinda99

Viessman is the one to go for (since you asked)

Brie

It's an Alpha CD28C.   Which a quick google shows as no longer being available.  No idea of installation date or when these were last being sold so can't do better on that front.  There is a label on the front of the boiler with the earliest return inspection date showing as in 2015 - not that that was necessarily when it was first inspected.  And it certainly has been inspected regularly since then.  I have no better information than that!

But I assume from the CD that it's a condensing one - which may or may not be draining into the plumbing somehow.  

We would need to stick to a combi I would guess as we're not about to start installing tanks anywhere.  We aren't high water use so no need for something extra fancy.

@macman said
Poor performance in the recent cold weather is not the result of  'low gas pressure'. If the rads are hot, then the issue is undersizing, or poor insulation.

With the outside temp currently being about 12c the rads are hot and we are cosy inside at 20c.   I agree that checking that the rads are the right size and the insulation is as good as possible will make this easier to maintain.

But when the temp was at zero the rads were barely warming up and the house was at 13c tops.  So there's something with the cold outdoors temp that is badly effecting things.  If there wasn't enough gas being delivered to the boiler it wouldn't be able to run properly.  Otherwise the cold itself is stopping the boiler from working.

Failure to maintain pressure is either a faulty EV (as explained above), a sticking PRV (easily checked by putting a bag over the external drain outlet to see if it's discharging), or a leak on the CH circuit. Only the latter takes more than 5 mins to diagnose, as it may not be visible. One of the first two are far more likely, and both are relatively simple components to replace. 

I wouldn't know where to start with any of that including where/how to check if it's discharging.  

If you've not had it serviced in 3 years, then now is the time.

I suspect then that is the good short term answer to get it serviced but it's possible the faulty/sticking/leak bits are what led the service guy to suggest a replacement the last time.  He did replace something somewhere but what it was I can't recall at this point.  I think that might have been 18 - 24 months back - unfortunately we've been a bit busy since then but I'm sure it was during lockdown as the boiler itself is outside and can be access without anyone coming in the house so there was no covid issues that needed to be sorted.  

BUT - my current issue is that when checking the boiler type I noticed the pressure needle is well beyond the top of the gauge rather than in the low green zone.  Does that tell anyone anything more??

macman

Yes, it's a 28kW condensing boiler. Manual here:
https://www.alpha-innovation.co.uk/custom/upload/instructions/CDC/CD25-28-35C Install & Serv Inst 30-07-10.pdf
The reason it won't obtain the target temp in cold weather is that the rate of heat loss from the house is massively higher with the much lower ambient temp. Many systems struggled in the recent cold snap, as they're just not designed for such extremes. This is not a boiler fault.
Gas pressure is regulated by a regulator fitted upstream of the meter, if it fails the boiler would shut down. 
If the pressure is now above 1.25 bar then you need to bleed any rad to reduce the pressure back into the green, and check that the filling loop is closed. You should correct this straight away.
There are only two wastes from a combi, one is the condensate pipe, usually to an outside drain but sometimes into a domestic waste. You want the other one, usually just a short projection through the wall to discharge in emergencies. Bagging that for 24 hours will reveal any discharge from the PRV.
But, if it's now going over-pressure, then that indicates that it's more likely to be an EV issue. Get it fixed without delay, as once the pressure reaches about 3 bar, the PRV will lift, and often they don't then seat down properly. again and will need replacing.
Do you not have the service record sheet to tell you what was replaced 18m ago?
These parts failing on a 12 year old boiler are to be expected and do not on their own justify replacement. Your RGI is doing a sales pitch if he said otherwise.