Heating Issues - Combi (ufh and rads)

[Burkle]

Just to note - i have a similar topic in the Radiators Section - the below is a further summary follow this now the ufh has issues. 

 To run through briefly what has been carried out:

- all radiators valves (TRVs and lockshields) changed

- x400 in system for 4 weeks and heating run as best as it would 

- central heating pipework main flushed (2 radiators removed and flushed individually) and the ufh heating loops (4 loops) mains flushed - all run through fine

- boiler pump replaced

- diverter valve pins / washers replaced and greased

- dhw water heat exchanger cleaned out (no issues at any time with hot water anyway)

- temp sensors replaced along with actuator motor on the combi 3 way valve in the boiler

- primary heat exchanger removed and flushed through; has now also been replaced along with seals to chamber 

 

The main issue is the heating does not get hot. There seems to be flow in the system as you can hear and feel water going through, and on the ufh you can see there is flow. 

 

Initially on calling for heat with the radiators they will get warm, then the burner will go off and pump still seems to be working and water flowing but it is colder. 

 

After removing the primary heat exchanger, cleaning this, then reinstalling, the ufh worked like a dream again!.... but only for 1 night, then the day after everything the same - hence why the primary heat exchanger has now been replaced suspecting the old one just may have had too much limescale and the like lodged in it. After replacing the heat exchanger, initially the radiators all worked great for an hour or so, similar to when the old one was cleaned.... then back to how it was before. 

 

Boiler fires on calling on either the UFH or central heating - diverter valves on both open up fine and seem to have no issue. 

 

Since changing the pump (for the same model / type ) the pump does whine / whistle when the ufh is on and the boiler is firing, but this goes off when the central heating is on with it at the same time, and the mixer valve at the manifold also whistles (the only way to stop it is turn the mixer down to minimum... but then the temp is just cool water). 

 

When feeling the pipework you can feel when the hot water pumps out the boiler, but there are several minutes between this happening, sometimes even say 5-10 minutes, and then it is just a flush of hot water. 

 

As the hot water works with no issues at all i am trying to find what the issue is before i make the decision to replace the boiler.

 

Any thoughts or advice would be much appreciated. 

[sharpener]

21 hours ago, Burkle said:

Initially on calling for heat with the radiators they will get warm, then the burner will go off and pump still seems to be working and water flowing but it is colder. 

 

From this it sounds to me like a control issue that is preventing the boiler from continuing to fire, might be internal to it or external but in view of what you have already done probably electrical not hydraulic.

[Nickfromwales]

I had an issue like this a while back with a Worcester Bosch combi, did my head in finding the fault, but eventually I just set my ‘magic’ electric test pen on the wire supplying 230v to the integral pump and hey presto…..intermittent fault on the PCB. The relay that powered the pump was failing, but had not failed fully, so it was giving a on/off output and the pump was starting and stopping in a random pattern (indicated by the led light in the test pen going on and off which was giving me a visual confirmation).

 

It was very hard to find this fault tbh as for some strange reason the pump was nowhere near as sporadic in operation when servicing DHW, but these things are sent to try us!
 

My assumption was that it was easier (less current draw through the relay) to pump locally to the PHE than it was to pump to 10 rads, therefore the failing relay was more ‘reliable’ on DHW and less when running heating.

 

Changed the PCB and problem solved.

 

Time, labour and parts costs to fix an old Biasi is a wasted investment imho, sorry, and if you now have to change the PCB to eliminate that then you’ve forked out a lot of dosh on an old boiler. Sadly this sounds like an on board control issue, bearing in mind I’m not there to test and trial it so is my best guess, so likely the PCB would need to be changed so it can be ruled out.

 

This could also be the same issue caused by the relay operating the gas valve, or the gas valve itself. 
 

It could also be the air switch on the fan, or the fan itself, or either of those relays……..

 

My advice on the other thread was to not put good money after bad, and I’m sticking with that advice. Abandon this boiler and fit a nice, quality brand, new one, possibly you may get some help or a grant depending on your circumstances. Call citizens advice to rake through all the schemes out there and see if you can get any help towards this.

 

I shudder to think what you’ve spent so far….and you probably have changed all the parts except the one(s) that’s broken….

[Burkle]

Thanks sharpener, and thanks Nickfromwales, i will check have a check on the wires during operation with a fluke pen to see if this is similar to what you found. 

 

I dont disagree with you on replacing the boiler, that is the next port of call! Labour thankfully hasnt cost anything in monetary terms (just my time!), and parts have all been reconditioned as they are generally now available new on this so its not been any more than £150 to date.... which it would likely have cost me more in getting somebody out to try and find the fault in the end anyway. I am just the sort of person who likes to understand how things work, and try and understand if it doesnt and why! Hence why all of this advice is great, but also shows that every situation can be different even if you can understand the workings. 

 

In the process at least i've flushed the system and all the radiators valves have been changed! 

 

The aspect i cant figure out so much still though is why the boiler is whistling / whining (sounds like the pump, but could be something else) only when the ufh is on / open and not when the CH is on or hot water. The pressure on the gauge for both the manifold and the boiler remain constant, and the ufh manifold shows there is flow during this. I did put the old pump head back on last night to see if this changed anything, but it still whistled. I also changed to the old pump body with the newer pump head to see if this made a difference but it didnt. It never used to make this noise, so that makes me wonder whether its the diverter valve which has had the insides replaced at the same time as the pump is the issue with the noise. 

 

In the process of speaking to a gas engineer on a replacement boiler

[sharpener]

22 minutes ago, Burkle said:

The aspect i cant figure out so much still though is why the boiler is whistling / whining (sounds like the pump, but could be something else)

 

Pumps complain like this when the flow is throttled, maybe the CH circuit is more open than the UFH. Or it might be the ABV opening (assuming there is one).

[Burkle]

Hi sharpener, yes there is an ABV between the flow and return after the ufh was installed over a year ago. No flow through the ABV when it is whining though, and no change in the whining

[SimonD]

2 hours ago, Burkle said:

boiler is whistling / whining

 

It could just be the fan. When you switch on ufh fan speed increases slightly to compensate for addition load.

[Nickfromwales]

3 hours ago, Burkle said:

that makes me wonder whether its the diverter valve

May be the integral automatic bypass valve, if the boiler has one?

[Nickfromwales]

3 hours ago, Burkle said:

In the process of speaking to a gas engineer on a replacement boiler

I don't give up easily, I assure you, and if it was any other boiler or newer I'd say hang in there, but pouring money into a budget (and old) boiler such as a Biasi is like paying expensive vet fees to squeeze 2 more years out of your favoutite goldfish.

[marshian]

12 minutes ago, Nickfromwales said:

I don't give up easily, I assure you, and if it was any other boiler or newer I'd say hang in there, but pouring money into a budget (and old) boiler such as a Biasi is like paying expensive vet fees to squeeze 2 more years out of your favoutite goldfish.

 

🤣 🤣 🤣

[Burkle]

2 hours ago, SimonD said:

 

It could just be the fan. When you switch on ufh fan speed increases slightly to compensate for addition load.

It never used to do it before the diverter and pump where worked on, that's what puzzles me

[Burkle]

1 hour ago, Nickfromwales said:

May be the integral automatic bypass valve, if the boiler has one?

It does have one out from the diverter back to the back of the return / pressure release valve, and it often gets too hot to touch 

[Nickfromwales]

1 hour ago, Burkle said:

It does have one out from the diverter back to the back of the return / pressure release valve, and it often gets too hot to touch 

Probably opening when the UFH is the only demand, and has been doing so for a long time, as with the UFH (as mentioned above) the flow from the boiler pump is firing against a brick wall (when UFH is doing very little / house nearly at temp and just one stat is still calling) unless the bypass valves take the strain and open up. Issue is, they just get worse at closing fully as time goes by.

 

I also do not ever fit those types of UFH blending valves as they are notorious for making squealing noises when the hot in / hot out ratio is close or equal. as they try to strangle the flow; this is at it's worst when it's a decent house with very low temp required or the UFH flow to the loops.

 

The knock on effect of that 'water hammer' (in essence) is that is gets sent hydraulically back through the system and wakes up any other valves or parts which want to sing in harmony.

 

UFH is often fitted very carelessly, and I have seen some installs that you'd think I was making up just how shite the install / setup / plumbing to and from was, and that's not getting started on the number of jobs I have visited that just should NEVER had UFH in the first place (70^oC flow into the loops and the rooms at 17^oC and no more).

 

If the boiler gets changed or fixed, I'd still want a piece of 22mm pipe bridging the flow and return at the UFH, installed as close to the UFH pump as possible, on close couple arranged tees, so the boiler can just whizz back to itself with zero resistance. An ABV is just unnecessary tbf, and the tee in arrangement will work wonderfully well at completely hydraulically separating the boiler flow from the UFH flow.

 

A lot of people forget that the UFH manifold pump is sucking water through the TMV vs pushing it through. It is free to ignore the TMV and recirculate without effort, the same scenario which you should be creating for the boiler pump.

 

I fear lots have been fixed / interfered with here, instead of the culprit, and this has woken the 'old gas boiler gods' and made them all angry.

 

I have to strip my Ariston combi next week as the PHE has started to dribble, and I bet that ends up in the skip and me in therapy.

[Burkle]

2 hours ago, Nickfromwales said:

 

 

If the boiler gets changed or fixed, I'd still want a piece of 22mm pipe bridging the flow and return at the UFH, installed as close to the UFH pump as possible, on close couple arranged tees, so the boiler can just whizz back to itself with zero resistance. An ABV is just unnecessary tbf, and the tee in arrangement will work wonderfully well at completely hydraulically separating the boiler flow from the UFH flow.

Something like figure 3 in this image 

 

thank you for a thorough explanation of everything too! 

[Nickfromwales]

22 hours ago, Burkle said:

Something like figure 3 in this image 

 

thank you for a thorough explanation of everything too! 

Yup, that's the kiddy.

 

That should make the (new / old whatever) boiler very happy and let it go on to live a full working life AND enjoy retirement   

[Burkle]

I will have a proper look when I'm home, but not sure there will be enough space available where the pipes have been dropped down in a corner. Might be able to make a primary flow circuit in the first floor under floor boards before they drop down as secondary (secondary flow pipes are going to be around 3m away though then). 

 

[Nickfromwales]

33 minutes ago, Burkle said:

I will have a proper look when I'm home, but not sure there will be enough space available where the pipes have been dropped down in a corner. Might be able to make a primary flow circuit in the first floor under floor boards before they drop down as secondary (secondary flow pipes are going to be around 3m away though then). 

 

Post a pic so we can make some suggestions. 👍

[JohnMo]

Guidance on close coupled tee install dimensions, so you get proper hydraulic separation.

 

[Burkle]

These photos show the current arrangement under the boiler upstairs with the ABV, and then the arrangement at the manifold downstairs 

[Nickfromwales]

@Burkle

 

Quick swap and not too hard to do.

 

 

[Nickfromwales]

If this was to be the 'ultimate spec' conversion, then between the 2 close-coupled tees would be another 2-port motorised valve that is "normally open". This would stay open until it was energised by the brown wire that provides signal to the radiator motorised valve.

 

The worry would (could) be that, if there is this permanent bypass loop, when the rads are on that may allow the boiler to ignore some of the rads or decrease the flow to them more than you'd want.

 

The second 2-port would allow the system to toggle between UFH only (with the valve open to allow the boiler to recirculate) and UFH + RADS (with the valve closed) to return this to the way it's currently plumbed).

 

This sounds like overkill, but it's actually the correct way to set this up without a buffer or low loss header.

 

Soooooooooo many plumbers just don't get it; that they set things up which appear to work "fine" on the day, week, month or year(s), but the setup is on borrowed time from day 1 as so many parts are functioning under duress.

[Burkle]

There is the current 2 port valve (the snug lite) for the ufh on the flow, then the CH circuit valve under the boiler on the flow after the t off to the ufh flow.... so if i read correct, ideally the 2 port valve on the ufh circuit would be between the close coupled t's (open with ufh all the time), and would be closed if both the CH and UFH are on... that way there will be a circuit to the CH open at the same time the UFH is on a loop, but if only the UFH is on then there is a bypass on with this. 

As you can see there isn't space for this, and the manifold can't move, but might there be anything to help this with the current ABV set up? Obviously currently the ABV is there whether the UFH is on or the CH or both, and I presume in reality the setting of the ABV would be different if you treat both individually.

Sorry for all the questions! I have a basic understanding of how the circuits can and would work, however I don't have the experience of it! If I am replacing the boiler I'd like to try and ensure the system is going to function.

 

 

Just as a side note (whilst I'm waiting on people to see and quote for boiler replacement), I've stripped down the diverter valve again and put all the old parts back in but cleaned up with the washers from the newer parts. There is no longer any whining / whistling, and the CH seems to be working OK (albeit, the system still needs balancing properly since all rad valves got replaced). However, the UFH circuit now cuts the boiler after around 10 minutes with either safety stat fault or primary circuit fault. I've tried increasing the UFH pump speed and decreasing it but both seem to be the same. The water gets through as the manifold gets warm. It's presumably a flow issue, and another reason for trying to ensure the actual circuit is OK before just replacing the boiler 

[Burkle]

Just to add, there is constant power to the pump on this too when I've sat checking, it doesn't stop during operation 

[Burkle]

7 hours ago, Burkle said:

Just to add, there is constant power to the pump on this too when I've sat checking, it doesn't stop during operation 

CH and UFH both worked no issues this morning. Only obaervation I have from the diverter valve is that some of the pins in the diverter kit where slightly longer than the older ones. The older ones may have worn slightly and the system become accustomed to this over time, then the subtle change with the newer ones cause whining with the water pushing through. 

Still looking to replace, but just in case anybody ever gets a similar issue 

[Nickfromwales]

11 hours ago, Burkle said:

As you can see there isn't space for this, and the manifold can't move, but might there be anything to help this with the current ABV set up?

I’ll have another look at space / options and reply a bit later 👍