Baxi eco 80 DHW issue

[Leeds222]

Hi. Hope I can find someone who's had this issue.
Baxi eco 80 DHW gets hot when water pressure is low, new HE fitted and both diaphragm's on diverter valve changed but still no better.
I did notice when CH on diverter valve (horizontal) for CH pin comes out and hits the limit switch and DHW stays in.
When DHW is turned on both the DHW and CH pins on diverter valve come out, is that normal?.
Totally lost with it now..
Don't want to replace the boiler as it's doing what it should do just not efficiently, rads warm up nice though, I believe also the hot water works better when heating is on but both diverter valve diaphragms have been replace 2 weeks ago.
Please help...

 

[Gasguru]

Your posting is confusing but I'm assuming the plate heat exchanger at the back has been replaced.

The pin at the front of the diverter only comes out with a hot water demand.

The pin on the top of the diverter comes out with either a heating or hot water demand....it's a safety device and tells the boiler electronics that the pump is operating and the boiler is full of water and circulating.

Do you mean the hot water is only hot with a low flowrate?

Open the hot taps fully, turn the boiler hot water temp control to maximum and gas rate the boiler, ie. calculate the gas consumption. See the FAQs item number 6 and post the result.

 

[Leeds222]

Hi. Yes it's the plate exchanger at the back which was replaced.
So seems the diverter valve is ok if you say both pins should operate the limit switches when DHW is demanded.
The boiler was tested a few weeks ago and I was told all was ok with the gas pressure/flow.
If I open a hot water tap fully the hot water does not hear up but if you restrict the flow by closing the tap it does heat up.

 

[Gasguru]

If the flowrate is too high no combi on earth will heat the water to a sufficient temperature.

You boiler will heat the water by 35 degrees with a flowrate no more than around 10 litres/min. So if the incoming water is 10 degrees then opening the tap to give a flowrate more than 10 litres/min will result in to lower a bathing temperature.

Have you checked that when using the hot water the LHS flow pipe to the radiators does not get hot. It may gradually get a little warm through conduction but any more than that and you will need a new diverter. Most of these boilers will however have had their diverters replaced by now.

 

[Leeds222]

The flow rate is quite low as in the upstairs bathroom it's not sufficient enough to keep the shower plunger open on the mixer taps.
Even though the diverter valve has had new diaphragms on both CH and DHW and both pins are operating can the diverter valve still be an issue.
I have noticed the hot water is warmer when the CH is on.
Thanks for helping me with this, still some kind people in this world.
I just can't think of any other component which is causing this, I would have thought the plate HE was the prime suspect but I was proved wrong again.

 

[Leeds222]

Sorry may have worded wrongly.
Flow rate is low as I've turned turn the water pressure to enable the water to heat up, if I open the mains water it just does not heat up the DHW at the taps so due to me turning down the water pressure there's low flow up stairs.
If I open up the mains water pressure is ok but cold

 

[Gasguru]

Open up the stopcock, open the hot taps fully and gas rate. Post results. Check the diverter as mentioned before...does the flow pipe to the rads get hot?

 

[Leeds222]

Hi
Thanks, I will try this today.

 

[gas112]

Diverter need stripping out and pin cleaned , seating cleaned and silicone grease applied

 

[Leeds222]

Ran hot water only with mains fully open, the CH feed warms up slightly but this is probably because it's next to the DHW feed but return on CH is cold.
Hot water only when mains pressure low or tap only opened slightly.
It's as if the boiler is too small but it's been in 15 years.
The boiler was removed and refitted last year and was off line for 4 months due to decorating.

 

[Agile]

No one can tell what is the problem is without proper scientific information.

1. Please measure the actual hot water flow rate in litres per minute!

See the FAQ if necessary!

2. Run the hot water when the radiators are cold and see if they start to warm up after about 10 min.

Tony

 

[Gasguru]

Leeds your wasting my time..just do what I say.

 

[Leeds222]

I as mentioned earlier opened the stop cock full and all hot taps up and downstairs.
Operating pressure 20mb
Heat input 25kw
Outlet to CH from boiler is Luke warm
Return pipe into boiler is cold
Sorry if you think I'm waisting your time

 

[Agile]

No one can tell what is the problem is without proper scientific information.

1. Please measure the actual hot water flow rate in litres per minute!

See the FAQ if necessary!

Tony

And the answer to this???

What exactly is the 20 mb "operating pressure"?

 

[ianmcd]

it seems that you simply have too much of a flow rate on the HW, as mentioned measure it, not a hard thing to do, then restrict the flow rate at the boiler rather than the main stop cock and you should be fine