Baxi Combi 80 HE Plus - return pipe doesn't fit

[Gasguru]

GC 47 075 16

The heating is non-existant, DHW performance is poor and the pre-heat takes forever. Typical sludged up system.

The main problem however is the return pre-formed pipe connection between the return isolating cock and the lower connection on the pump back casing.

I removed this pipe to gain access to the return filter located in the isolating valve. When I replaced the connection pipe (it also has the pressure gauge tapping) and locked the O ring seal into the pump housing with the screw the lower flange was 8mm short of the isolating valve.

1/2 Hour on the phone to Baxi got no where. They deny this part was sent out too short. In the end I used 3 fibre washers to make up the gap with the O ring just sealing (but not locked in with the screw). This is how it was previously installed by the cowboys 2 years ago. The other odd thing is the PRV pipe from the valve to the wall jig. This has an end feed coupling soldered to extend the lenght - were these also formed too short?

Any Baxi regulars any idea? The boiler is definately fitted to the wall jig correctly (if it wasn't the other connections wouldn't fit properly).

The image shows the pipe packed out with washers, the O ring joint is not fiully pushed home and the boiler pressurised just enough to get hot water.

 

[Agile]

Isnt the return filter under the boiler and accessed from the front without disconnecting anything else?

The salient question is what was it like when you disconnected the pipe in the first place?

Are you quite sure the boiler frame is not distorted?

Tony

 

[Gasguru]

There is zero flow to the rads even after the return filter clean. The nearest rad 6 foot away has a LS and WH valve - stone cold.

This is the boiler with a flow pipe switch so all rads should have TRV's for compliance unless a conventional room stat is fitted (not done on this installation)

The customer has already been ripped off by the original lot. It now looks as though all the existing TRV's (Vaillant with female compression joints) need changing, all LS valves changing (bound to leak), complete powerflush, plate heat ex cleaning, new diverter, pump impeller checking and this problem with the return pipe.


The return filter sits inside the top "thread" part of the isolating valve.

The original installers had packed it out with just two fibre washers and the O ring joint was not locked in place. How it has not leaked is down to luck.

I can't see how it can distort 8mm - the other connections line up and there is no "give" on those ie the connections are from the IV's to the moulded manifolds. The wall jig and main chassis measure the same on each side.

Checking on Partsarena shows a "isolation cock rectification kit" but Baxi deny any problems. There are no proper details of this kit.

 

[baxpoti]

From your picture, the jig appears to bowing, the return locking nut is dropping away to the left and front, compare it to the PRV locknut

The jig is either not on a flat surface, or not squarely fitted (the pipe connections are pulling it down and twisting it)

When re-fitting pipes loosen all the locknuts, do up the pipe connections and re-tighten the lock nuts.

 

[Gasguru]

The camera lens is distorting the image slightly.

The upstand just behind the locking nuts prevents the horizontal surfave fom bowing. The cold inlet pipe to the left of the return connects straight into the flowswitch. Without taking the plate exchanger off I can't see whether this too has been bodged.

When I compare measurements between boiler chassis and wall jig on each side there is no indication of any distortion.

On another point how can the TRV's on all rads coupled with the flowswitch ever work - it appears a flawed design. Baxi have obvioulsy done this as an alternative method for compliance with Part L Building Regs (and make it potentially cheaper for installers since many installations require a new roomstat/lockshielded rad).

What happens when the rads progressively shutdown - plenty of noise from excessive differential pressure across the TRV's. The boiler should have been designed with a modulating pump since an ABV can't be used as it would stop the flowswitch shutting down the boiler.

 

[baxpoti]

The camera lens is distorting the image slightly.

possibly

The upstand just behind the locking nuts prevents the horizontal surfave fom bowing.

no it doesn't, I've seen these twisted by heavy handed over tightening (using a pair of grips rather than a correct size spanner).

Without taking the plate exchanger off I can't see whether this too has been bodged.

probably

how can the TRV's on all rads coupled with the flowswitch ever work - it appears a flawed design.

It works! and has done since 1998 long before Part L. Flow switch (boiler interlock) will drop out at approx 2½Lts/min

Sounds like you do have a real botched installation.

 

[Gasguru]

But what happens when only one TRV is open (the rest have shut down) - a 6 meter pump on speed 3 will create excessive noise.

No TRV manufacturer would advise doing this without fitting a bypass it contradicts good practice.

 

[Agile]

Regarding the possible distortion Geoff, did you measure the diagonal distances in case of trapezoidal distortion?

Are there loose locknuts above and below the chassis plate or is there a fixed flange underneath?

Do I understand you correctly that the filter is accessed from the nut in your first picture? If so one wonders why they have changed from the horizontal filter underneath or is yours a predecessor?

I do some warranty repairs so I get to see the odd two or three boilers in a thousand with a problem and have never seen anything like that ( yet ).

Tony

 

[baxpoti]

But what happens when only one TRV is open (the rest have shut down) - a 6 meter pump on speed 3 will create excessive noise.

Probably would on a poorly designed system with cheap TRVs

No TRV manufacturer would advise doing this without fitting a bypass it contradicts good practice.

If you say so! you would need another boiler interlock fitted.

 

[baxpoti]

Are there loose locknuts above and below the chassis plate or is there a fixed flange underneath?

Fixed flange, the isolation valves also have lock nuts and fixed flange (lots of room for movement.

Do I understand you correctly that the filter is accessed from the nut in your first picture? If so one wonders why they have changed from the horizontal filter underneath or is yours a predecessor?

The filter is (should be) under this nut and always has been.

 

[Agile]

The filter is (should be) under this nut and always has been.

That is not a good design because the dirt comes up into the filter and can then drop back down into the valve underneath ( unless you are clever enough to take the valve off first! ).

The horizontal filter accessed from the front is a much better design apart from being too small to hold much dirt!

Tony

 

[Gasguru]

I think Baxi suffer the way most large companies do - no one talks to each other and you get some good design and some rubbish. This boiler is horrible to work on. I was initially told it was a different model the Band B with recuperator, had I known it was this model I would have turned the job down.

The IV's have a flange that is pulled tight up against the lower face of the jig with the locknut. With no movement on the tails I doubt the filter could be removed without cutting out the pipework. I guess this boiler was designed in the UK - ie full of ill-thoughout design.

As for measuring - very difficult - I suspect I'm going to have to take the boiler off the wall. Customer paid £1900 for just the boiler swapout 2 years ago. The company claims to have powerflushed - no way with the crud in the system.

Even quality valves - Honeywell, Danfoss or Drayton will all exhibit noise if the pressure is sufficiently high. Comparing specs is difficult but the manufacturures literature specifies the need for auto bypass and that has always been my experience.

Baxpoti, what valves do you recommend for a quiet system. The last thing I want to give the customer is more problems.

 

[baxpoti]

Baxpoti, what valves do you recommend for a quiet system. The last thing I want to give the customer is more problems.

I'm not recommending anything, but my system at home is fitted with Honeywell VT117Es, - never hear 'em.

 

[Gasguru]

Honeywell it is then (although Danfoss max diff pressures are similar and plenty have complained about noise if no ABV fitted).

 

[baxpoti]

Extract from the installation instuctions

This boiler is fitted with a flow switch interlock that prevents it from firing when the heating demand is satisfied.

The boiler is designed so that it will heat the house to the desired room temperature as quickly as possible by running at the maximum radiator temperature of 82°C. Once this room temperature is achieved the boiler will then reduce the radiator temperature to as low a level as possible, while still achieving the desired room temperature, thereby giving the most efficient use of gas and the most comfortable room temperature possible.

The boiler will be able to achieve this performance if a room thermostat is fitted or with a fully TRV'd system without a bypass.

This boiler does not require a bypass. To comply with Part L1 of the Building Regulations the heating system into which the boiler is installed should include the following:

a) zone controls

b) timing controls

c) boiler control interlocks

Such a system needs to be fully pumped and must provide independent temperature and time control to both the heating and hot water circuits and have a boiler interlock.

The boiler should be controlled so that it operates on demand only. Where it is proposed to effect control by thermostatic radiator valves, a room thermostat (or other device such as a flow switch - a flow switch is integral to this boiler) should also be provided to switch off the boiler when there is no demand for heating or hot water.

The interlock for CH circuit can be provided in either of the following ways:

a) A Room Thermostat with at least the radiator nearest the room stat not TRV'd.

b) A fully TRV'd system without a bypass.

A fully TRV'd system with a bypass that has not been valved off does not comply with Part L1 of the Building Regulations.

If the system is fully TRV'd with a bypass then this feature will not be available, in this case the radiator temperature can be reduced to provide more efficient operation.