GRANT COMBI 90 MK11 which has a very low hot water flow rate.

[jayjac]

hi can anybody help? I have a GRANT COMBI 90 MK11 which has a very low hot water flow rate.
static hot water pressure at the taps is approx 2 / 2.5bar but flow rate is very poor. Water pressure at meter on cold is 2 bar with flow rate 30 lt per min and good cold pressure and flow in the house. Boiler has had recent service, new heat exchanger and what looks like a new therm mixing valve along with new pipework from boiler to kit/bathroom. Heating works fine and hot water is hot just very very slow, takes hours to run a bath. My local heating engineer says its the heat exchanger but thats only 2 months old. HELP NEEDED PLEASE cos my better half is giving me a right ear bashing



Read more: //www.diynot.com/diy/threads/low-hot-water-flow-rate.439630/#ixzz3hxfhhHWE

 

[oilhead]

If the hot water flow is significantly lower than the cold flow, then there must be an obstruction somewhere in that circuit. When you say you have had what looks like a new mixing valve, if it is not, then this could be your problem. Alternatively, there may be a blockage in the supply pipework that has been renewed. Can you see whether the microswitch is operated by the diaphragm?

 

[jayjac]

Hi thanks for that, I can't see or detect any visual movement around the diaphragm or switch however the system change's from heating to hot water only with no apparent problem's so I am guessing that's ok. I will take a look at the mixing valve next to see if that's clear and then check the pipework again.
Thanks again for the help and advice.

 

[oilhead]

If you cannot see movement in the microswitch, then the diaphragm is not moving. This suggests that the supply to the boiler is insufficient, taken with the low flow performance.

 

[muggles]

There's often a flow adjustment valve on the inlet to the heat exchanger on these - post a photo of the heat exchanger and the pipework going into it

Be aware, though, that hot water flow rate will always be lower than cold water flow rate - that is the nature of a combi boiler

 

[jayjac]

Hi all, It looks like it was the mixing valve furred up around the filters so all cleaned out and much better water flow now, it's still not great in the bathroom but I think that is just the nature of the beast. A huge thank you to Oilhead and Muggles for all your help and taking the time to reply as I would not have sorted it without your help.
PS I now have a happy misses who also say's THANK YOU