Vaillant 937 Hot Water Flow step change?

[Tipper]

Hi, today the HW flow produced by our Vaillant 937 (2008 install) has dropped to the point where running a bath is a joke. What's happened to cause this? Cold pressure and flow is OK but hot starts off good for a second then eases right back to about a third flow.

Is the plate heat exchanger blocked or is there a filter somewhere that needs cleaning? Could be a delivery pipework problem too I suppose.

Any suggestions gratefully received before I call our local Vaillant man in next week.

Thanks

 

[Bunnyman]

Does it do it on all taps or just the bath?

 

[Tipper]

Upstairs only, kitchen sink appears to be OK. Therefore I suspect we may have a piping problem.

Some of the original pipework is in copper but when the boiler was installed plastic with speedfit fittings was used by the installer. I have to say I have always suspected that the speedfit sleeves produce an unnecessary restriction at the fittings unlike Hep which are larger bore.

I can't remember whether the mixer taps in the bathroom have inlet filters or not.

Looks like I'm going to have to strip part of the HW system down to find the problem.

Are there any filters in the boiler on the DHW side though?

 

[Agile]

If its only at the bath tap then it sounds as if the bath tap may be faulty or there is some debris blocking it.

I would be asking you to be measuring the flow rate in li/min from each hot outlet in turn! And then with all open and added together!

Tony

 

[Bunnyman]

As agile said its probably ur bath tap, if the jumpers broke the tap opens an flow is ok then as the hot water hits the jumper washer it swells up a causes flow to reduce on its own, check that first

 

[Tipper]

Just the bathroom at the moment and if the bath tap is opened it initially runs well, but just for a few seconds and then drastically reduces in flow rate. Opening the basin tap that is fed from the same pipe causes both to almost stop running!

I think it's probably the supply pipe to the bathroom that is the problem. But why all of a sudden? We are in a soft water area so no scale issues normally occur but my wife says she has seen some soft scale like lumps coming from the taps.

Both bath and basin taps are Grohe, i.e. expensive, ceramic disc mixer taps.
Oh and the mixer shower fed off the same pipe but before the bath and basin is not affected.

 

[Agile]

Right so now we are getting closer to the problem.

Both bathroom taps give the problem.

Apparently a blockage in the common supply pipe.

Bits of debris can float around the pipes an bits of foam insulation or glass fibre bits and sometimes block and sometimes unblock.

A simple non intrusive try would be to force mains water back up pipes from bathroom towards the kitchen ( with the boiler output isolated ).

Tony

 

[Tipper]

Finally found time to investigate further on this prompted by the problem getting worse and complaints becoming more frequent!

This morning ALL hot taps are affected not just the bath/basin in the bathroom. So whatever the problem is it's got worse.

I've also established that the cold supply to the boiler is OK as there is a hose tap below the boiler due to the boiler being in the garage below the house. Plenty of flow at that tap.

So it's either the pipework from the boiler to the first takeoff, which is to the kitchen and cloakroom, or it's the boiler itself.

Later today,and tomorrow, I will investigate further to establish what's going on. I plan to disconnect the HW at the boiler and temporarily supply the pipework with cold to first check if the pipework is the problem. If that's OK then it must be something in the boiler.

Any suggestions?