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Westinghouse (HTP) combi boiler DHW output fluctuating

I have the Westinghouse model WBRCU floor model combi boiler on natural gas. 140,000 btu. In the warmer months it works flawlessly. As soon as there is a call for heat the DHW fluctuates all over to where you constantly have to adjust the shower handles. I reached out to tech support last season and they had me remove my outdoor temp sensor and change several of the curve setpoints. It’s my understanding that this shouldn’t have anything to do with the DHW water temp. It should ignore all those settings when there is a call for DHW. They were no help and at least the guy I spoke with didn’t seem very knowledgeable. Is anyone familiar with this units or this issue. Thabks. MRkp

Comments

  • Ironman
    Ironman Member Posts: 7,076
    edited November 2022
    You’re correct that the OD sensor has nothing to do with domestic and you should re-connect it to save energy.

    The plate heat exchanger may need de-scaling, particularly if you have hard water.

    The 3 way change over valve may also be the issue.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • styxplo
    styxplo Member Posts: 54
    This is only the 2nd season. The heating side has treated DI water and our water is filtered and softened. I can clean the heat exchanger but it should be good. It worked good until about 1-1/2 weeks. Last year I was thinking that maybe the ground water got colder, but that isn’t the case. 
  • hot_rod
    hot_rod Member Posts: 18,210
    Take the cover off and watch or meter what is going on. As Bob mentioned, first a 3 way zone or solonoid valve needs  to move to DHW and stay there. Does it?
    Boiler needs to ramp up temperature. Then the small HX needs to have adequate flow 

    Interestingly we are seeing those plate heat exchanger get scaled on both DHW and the boiler side if the fill water was hard or a lot of debris in the heating loop. Deliming sometimes needs to be done on both sides

    Easiest to remove the plate HX dot do both sides. Soak it in delimed acid, or take it to a radiator shop and have them “cook” it clean  I had a customer that did that to a plate HX every 2 years, he had a radiator shop across the street.

    Even with bare hands you can sometimes determine which side is not keeping up.

    Does it have a thermostatic 3 way mixing valve on the DHW?  Same scaling issue with them.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • styxplo
    styxplo Member Posts: 54
    Ok. I will look into it. No 3 way mixing valve on the DHW. Thabks
  • Ironman
    Ironman Member Posts: 7,076
    If it’s a combi, there’s a 3 way valve inside that switches between space heating and domestic.

    They fail quite often.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • BobZmuda
    BobZmuda Member Posts: 23
    Did you figure it out?  FYI supplyhouse.com has the 3 way valves for sale for the laars version. 

    The domestic hot water heat exchanger in this model is not a flat plate heat exchanger.  It’s a mini tank.  Which imo is a huge plus for multiple reasons, main two are less problems with scale and no hot water “sandwich” while waiting for the boiler to fire up.  Note that I said less problems with scale, not zero problems. 

    There’s also a flow restrictor on your model. That can scale up or otherwise become restricted. It’s supposed to be pulled out and cleaned every year. 
  • styxplo
    styxplo Member Posts: 54
    I haven't had a chance to look into it yet. I've been working 7-12's. I plan on checking it out over the holiday. Thanks for the info/update.
  • styxplo
    styxplo Member Posts: 54
    I looked into my issue today. The feedback temp for the DHW varies from 143 down to 120. The setpoint is 140. The flow varies from 1.38 to 1.68 GPM. The specs for the shower faucet is max flow of 2.5 GPM at 80 psi. I think this is because of my well pump kicking on and off (what is a good setting for the pressure switch at the pump?). Although it seemed that this problem only appears in the colder months which led me to believe it had something to do with it calling for heat, I'm not sure this is the case anymore. I turned my thermostat on and off during the test and it behaved the same either way. I see there is some kind of modulated mixing valve with feedback. Not really sure how to test it, but it appears to work correctly when its heating the CH water. As I was writing this email. I looked at the drawing and read the 3 way valve. I had solid 120v on the DHW side of the valve. As I was testing this the DHW stayed between 139 and 141. It did this whether there was a call for heat or not. Not sure what changed but I feel this is how its supposed to work. Seems to be intermittent.

    I did see that it comes with 2 flow restrictors and the lowest flow one is installed from the factory.